An adjustable dumbbell device includes one or more weight members and one or more weight elements each having two side panels to form a chamber, and an opening formed in each of the panels, two housings detachably engaged in the weight member and the weight element, two catches slidably engaged in each of the housings and engageable with the openings of the panels for anchoring the housings to the weight member and the weight element selectively, two followers are rotatably engaged in each of the housings and each include a gear engaged with the catches for moving the catches to engage with the panels and to anchor the housings to the weight member and the weight element respectively.