An adjustable dumbbell includes a base, a grip, and a plurality of sets of dumbbell plate assemblies connected on both sides of the grip. The dumbbell plate assembly includes a rotating member, an adapter, a limiting member and a weight plate. The rotating member rotates with the grip. The limiting member is located between the rotating member and the adapter. The limiting member fits with and is connected to the adapter in a non-rotatable manner. When the rotating member rotates, the rotating member abuts against the abutting rib to drive the limiting member to translate, so that the protrusion is inserted into or separated from the insertion hole to connect or separate the limiting member and the adapter.