The actress, most famous for her role as Ellen Ripley in the franchise, joined co-stars Bill Paxton, Michael Biehn, Paul Reiser, Jenette Goldstein, Lance Henriksen and Carrie Henn at the Comic and Entertainment Expo in Calgary, Canada.
The reunion was set up to mark the anniversary of the James Cameron classic, which was released in 1986, and the castmates admitted they are still blown away by how many film fans still ask them about the movie.
Paxton said, "They'll still be asking us about Aliens (in 100 years). Haven’t you people had enough?"
Weaver spoke about picking up a Best Actress Oscar nomination for her role in the film, and admits she was ill prepared for the amount of attention she received after playing Ripley.
She explained: "I was shocked. I don't think I really understood the significance of the genre, getting recognised like that.
“I was very, very honoured, but it was such an ensemble picture... I was really representing everyone. We were such a family."