Twitter currently limits tweets to 140 characters, but has doubled that to 280 characters for a small group of users.
The current character limit was "a major cause of frustration" for some users, the firm said in a blog post.
The firm has been suffering from slowing growth and the shift could be one way for the firm to widen its appeal and attract new users.
"Trying to cram your thoughts into a Tweet - we've all been there, and it's a pain," Twitter product manager Aliza Rosen wrote.
