A foldable chair comprises a chair seat, front leg tubes, rear leg tubes, and two telescopic frames. The two telescopic frames respectively correspond to the front leg tubes and the rear leg tubes. Each of the two telescopic frames comprises two support tubes and a connection tube connected to the two support tubes. The two support tubes of a first of the two telescopic frames are respectively and telescopically coupled with the front leg tubes, and the two support tubes of a second of the two telescopic frames are respectively and telescopically coupled with the rear leg tubes. A locking mechanism is disposed between each of the support tubes and a corresponding one of the front leg tubes and the rear leg tubes.