An optical fiber adapter according to the present invention includes a main body, an inner housing and a cover plate. The main body has an axial cavity 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. The axial cavity has two opposing axial openings and is configured to receive the inner housing. An access opening is arranged on the first wall for the inner housing to place within the axial cavity. A plurality of protruding portions is positioned on the second and fourth walls, respectively, wherein each the protruding portion has an indentation formed thereon and facing the access opening. The cover plate is configured to cover the access opening on the first wall of the main body, wherein the cover plate has a plurality of protrusions formed thereon and positioning corresponding to the indentations on the protruding portions of the main body. When the protrusions on the cover plate are melted and the cover plate is brought to cover the access opening, the molten protrusions will bond with the protruding portions of the main body.