An optical adapter includes a base body, a shutter member, and a supporting base. The shutter member is pivotally connected at an insertion opening of the base body. The supporting base is assembled on a bottom portion of the base body. A surface of the supporting base has an abutting piece inside the base body. One of two ends of the abutting piece includes a fixing portion fixed on the supporting base, and the other end of the abutting piece includes an abutting portion obliquely extending toward the shutter member to abut against a back surface of the shutter member. Therefore, the supporting base can be assembled on the bottom of the base body conveniently. Furthermore, when the abutting piece is pushed and compressed by the shutter member, the abutting piece is not prone to have excessive deformation, prevent the abutting piece from being deformed or damaged easily.