Abstract: Disclosed is a hair retaining device for preventing long hair of a wearer of the hair retaining device from getting tangled and damaged. The hair retaining device includes a cap member configured to cover a head portion of the wearer thereof, a pair of straps configured on a rear end portion of the cap member, a tail member extending from the rear end portion of the cap member, and a flap member configured on an inner surface of the tail member. The pair of straps is capable of securing the cap member to the head portion of the wearer thereof. Further, the flap member and the inner surface of the tail member configures a space therebetween for receiving at least a portion of the hair of the wearer thereof.