Weaver previously worked with James Cameron on the hit movie Aliens 
Sigourney Weaver's character fleshed out Avatar's environmental message Actress Sigourney Weaver says she will appear in the sequel to sci-fi film Avatar, despite her character dying in the first instalment."Don't worry, I will be back," she told US movie website Coming Soon.Weaver played botanist Grace Augustine in the 3D epic, which took more than $2.7bn (£1.7bn) worldwide.
Her character was fatally wounded in a climactic battle, but the actress said director James Cameron had told her "no one ever dies in science fiction".
"He's told me the stories for the next two movies and I have to say that they're absolutely wonderful," she added.
"Now we just have to make them."
The original Avatar, which told the story of humans mining an alien planet for reserves of the improbably-named mineral Unobtanium, is the highest-grossing movie of all time.
Director Cameron promised to turn the story into a trilogy if box office receipts reached $1bn (£633m).
Work on the scripts has begun but, as yet, there is no filming schedule.
When shooting commences, Avatar 2 and 3 will be made back-to-back, with months of post-production to create the computer-generated alien world of Pandora.
Speaking on the red carpet at the 2010 Oscars, Cameron admitted: "If I were to start Avatar 2 tomorrow, it would still be three years away".
He later confirmed that the first possible release date for the sequel was Christmas 2014.
"The boss, Jim Cameron, he's not just going to make it for the sake of it," actor Sam Worthington told Radio 1 Newsbeat last year.
"He always wants the challenge, he always wants to push the envelope and raise the bar and I think audiences will demand that of Avatar 2.
"When he finds the challenge that's when we go back to work."
