An adjustable dumbbell, comprising a dumbbell assembly, a dumbbell seat and dumbbell pieces, the dumbbell assembly comprises a dumbbell bar and connecting discs, which are provided with a positioning groove and a connecting block slidingly connected in the positioning groove, and the connecting disc is provided with an elastic component; the dumbbell assembly comprises a handle grip and gear blocks, and the glove and the gear block are fixed circumferentially, and the gear block has an outwardly pushing part and an inwardly shrinking part in the circumferential direction; the dumbbell piece is provided with a connecting groove, when the connecting block abuts against the shrinking part, the connecting block is separated from the connecting groove; the connecting block abuts against the pushing part, the connecting block is snapped into the connecting groove; when the connecting block abuts against the shrinking part, the connecting block is separated from the connecting groove.