A key device includes a key cap and a base plate unit. The key cap includes a top wall and a peripheral wall cooperatively defining a receiving space. The top wall has a plurality of spaced-apart studs protruding into the receiving space. The base plate unit is disposed in the receiving space and is riveted to the top wall through the studs. The base plate unit includes a base plate, and a plurality of engaging members secured to the base plate. The base plate includes a plurality of stud holes for extension of the studs respectively therethrough, and a plurality of spaced-apart anchor members. The engaging members are injection molded to the anchor members, respectively.