A dumbbell weight selection structure includes an extension rod disposed at any end of a handle unit. The extension rod is disposed with a selection unit, which contains a selection mechanism and multiple weight plates are disposed thereon. The selection mechanism includes a slide plate linked to drive the selection plate set to travel. A locking hole to insert by the selection plate set is disposed at where appropriately on each weight plate. The slide plate is moved to change connection of the selection plate set corresponding to the locking holes of multiple weight plates to select quantity of weight plates to be attached to the dumbbell as desired for achieving discretional adjustment of the overall weight of the dumbbell.