A weight adjustable exercise device includes a base unit and a handle unit. Two magnetically attractive members are spacedly disposed on the base unit. Two weight sets are supported by the base unit, and respectively have a plurality of weights. The handle unit includes a handle shaft, two anti-rotation modules non-rotatably sleeved around two opposite end portions of the handle shaft and insertable downwardly in the base unit, two weight adjusting modules respectively mounted on the anti-rotation modules, and two indexing discs rotatably mounted on the weight adjusting modules. Each weight adjusting module has selector assemblies rotated with the handle shaft to selectively engage with or be disengaged from the corresponding weights. Each anti-rotation module has a magnet member removably engaged with the corresponding indexing disc and movable by a magnetically attractive force of the corresponding magnetically attractive member to be disengaged from the corresponding indexing disc.