A protect cap for an optical fiber adapter according to the present disclosure is provided. The protect cap includes a casing defining a passage for receiving the optical fiber adapter, a pair of supporting lugs formed on the casing, a covering lid, and a pair of supporting arms extending from the covering lid. Each of the supporting lugs defines a shaft hole. Each of the supporting arms is provided with a shaft, wherein the shafts are positioned in the shaft holes, respectively such that the covering lid is pivotally connected to the casing. A first protrusion is formed on one of the shafts and a second protrusion is formed on an inner surface of one of the shaft holes. When the shafts are rotated to bring the first protrusion into contact with the second protrusion, the covering lid is kept in an open position with respect to the casing.