Hi every body..... I could not kill the rothalos ?

Ok, so as far I can tell, you die when you have the rathalos when he is weak. You can always tell when a Rathalos is weak because will limp and will most likely try to sleep and regain his health.

The first thing I recommend is to Pitfall traps. You can get pitfall traps by combining net and trap tool (to get net combine ivy and spiderweb). Bring with you these items to help you:

Potions and herbs
Power juices (calalyst and rare steak) so you can constantly run and block without tiring. antidotes, so you can heel yourself if you get posioned.
Barrel bombs and flash bombs, use them like you have been doing
1 pitfall trap ]
2 nets ]--- these items will altogether give you three pitfall traps to use
2 trap tools ]

What I do is when you begin the quest, go staight to the area with the velociprey that help the rathalos, and kill them first. It will mean they won't bother you when you have a weak rathalos to finish off.

When the rathalos runs to it's nest to recover health, lay down the first pitfall trap just infront of it as it is landing. Stand behind the pitfall trap so the rathalos charges into it. When it is stuck in the pitfall trap, get your weapon and hit it until it free's itself.

Wait until you have a free space and alot of time before setting down the next pitfall trap, for example just after the rathalos has fallen down after a charge. Stand behing the pitfall trap, in line with the rathalos and let the rathalos fall into the pitfall trap again, hit it until it gets out. Repeat for the last pitfall trap.

If the rathalos isn't dead by then it will be very near to death. You won't have much trouble finishing it off, seeming as you don't have the velociprey to bother you.

I suggest you upgrade your weapon or make a stronger one. I use the Iron Katana 'Gospel' and have no problem killing Rathalos using only my sword and some potions. Gospel is made by creating an iron sword then upgradeing to iron sword+ --> Iron Katana 'Grace' --> Iron Katana'Gospel'. For this you will need 15 iron ore, 21 machalite ore, and 40 earth crystals. To get the materials go to the four star gathering hall quest "Gathering - Desert zone". Go to area six and mine the three mining spots, after your done deliver the pawpass that is provided in the supplies box. After go to the Kokoto Farm and mine there. Repeat the process until you have enough ore. I know it sounds like a lot of work to get this sword but it will be worth it in the long run because it can be up graded into the Eager Cleaver that has thunder damage. Also a piece of advice don't waste your rathalos claws save them for the Redwing (Bone Blade --> Bone Blade+ --> Agito --> Agito+ --> Dragon Agito --> Redwing) it has fire damage.

Don't worry, rathalos is a hard wyvern to kill, although when I killed him it was quite spectacular as I used none of the recomended tactics, I didnt use traps or bombs or even flash bombs. the first thing I recomend changing is use a sword and shield, peope say they are really weak, but they are wrong, I can kill a kut-ku in about 30 seconds with a SnS. I recomend the poison battle axe, it has high attack power and a high poison rate and as all SnS's is very fast

The second thing I recomend is try to cut his tail off, not only will this give you more rewards at the end but will greatly decrease the range of his tail whip which I think is the most annoying of any wyverns attacks (i didnt when i killed him and i KNOW it would have helped)

Number 3 is try using FULL loprey mail armour, it has good defence amd negates poison which rathalos does has, also it has good fire resistance and that helps greatly (an easy way to get loprey materials is going multiplayer and doing the gathering hall loprey quest, this gets poison sacks for the recomended sword too)

Number 4 is go for the head if you can, if not go for the tail and belly, be careful when you are under him, he does an attack where he flies away backwards and fireball the exact spot he was standing in (where you will be)

Number 5 is make note of your movement, don't attack directly in front of his mouth, you may of seen his massive fireball, directly under him he can do variouse attacks on you, too far behind you get tail whipped,so I recommend attacking near his left leg but this is not full-proof, I think he can bite you from there, and also ROLLING AWAY CAN SAVE YOUR LIFE if you have ever fought that rock wyvern thats belly splits open when weakemed (i forgot the name basar-somthing I think) rolling is essential

Number 6 is try to use the pitfall trap large barrel bomb technique if you can, it can do quite a lot of damage, and try to use any other easy to do tacticts too if possible (i never did but I know it should help)

Notes: try to fight him as much as possible in areas 3 and 4 they are the easiest, run away to heal if you need to, try to dodge attacks as much as posible, keep your weapon in green sharpness, make sure to keep him paintballed

Well, from my experiance, this is enough to get you through this quest
Hope I helped
Bye!

P.s please take not of the SnS, they actually do more damage that great swords in the same amount of time if you are good, hopefully you will grow to love SnS's as I do! I've tried useing slvrfng serpant blade doing velocidrome, had to run and heal, with SnS won in about 10 secs of fighting