An optical fiber adapter according to the present disclosure includes a main body, an inner housing and a cover plate. The main body has an accommodation room in an axial direction defined by a first wall, a second wall, a third wall and a fourth wall, wherein the first wall faces the third wall and connects with the second and fourth walls. An access opening is arranged on the first wall. The inner housing may be inserted into the accommodation room through the access opening on the first wall. Two protruding portions extend from the second and fourth walls, respectively. The cover plate is configured to cover the access opening on the first wall, wherein the cover plate has a plurality of hooking portions formed thereon for hooking on to the protruding portions, respectively.