A fixing mechanism for fixing a disc drive and a locking device thereof solves the inconvenience involved in fixing and disassembling the disc drive. The disc drive has at least one a pair of protrusions located at side walls of the disc drive. The fixing mechanism includes a fixing frame and a locking device. The fixing frame has a pair of assembling walls and at least one receiving space is used for receiving the disc drive. One of the assembling walls has a pair of assembling boards protruding outward and an open sliding slot. The protrusions are slidably installed in the sliding slot. The locking device includes a base part and a locking arm. Two sides of the base part are assembled to the assembling boards. A locking hole formed at the free end of the locking arm correspondingly locks one of the protrusions of the disc drive.