A mount bracket connected to a slide assembly and installed to a post of a rack, the post having a plurality of holes, the mount bracket comprising: a fixing frame having a side wall, an end wall, and two protrusions (28a, 28b) respectively extending from a top side and a bottom side of the sidewall, the two protrusions (28a, 28b) and the side wall defining a first path, the side wall having a recess and defining a second path; an installation unit fixed to the end wall of the fixing frame; a movable member having a first board and a second board, the first board inserted into the first path of the fixing frame, the first board having a contact portion and a support frame, the support frame inserted into the second path of the fixing frame and the contact portion located adjacent to the second board, the support frame having an engaging hole, the second board having a plurality of holes which are located corresponding to the installation unit; a positioning member having a fixing portion, a resilient arm, an activation portion and an engaging portion, the fixing portion fixed to the side wall of the fixing frame, the resilient arm connected between the fixing portion and the activation portion, the activation portion extending an angle from an end of the resilient arm, the engaging portion located on the resilient arm and located corresponding to the engaging hole of the movable member; a release member movably connected to the first board of the movable member and having a push block which is located corresponding to the activation portion of the positioning member; and when assembled, the contact portion of the movable member and the second board are adapted to contact the inside and outside of the post of the rack, the installation unit is located corresponding to the holes of the post, the fixing frame is pushed toward the post to insert the installation unit into the holes of the post, only the engaging portion of the positioning member is engaged with the engaging hole of the movable member to connect the movable member to the fixing frame, and when pushing the release member, the push block of the release member contacts the activation portion of the positioning member, the resilient arm of the positioning member is lifted relative to the movable member, the engaging portion of the positioning member is disengaged from the engaging hole of the movable member, the movable member is movable relative to the fixing frame, the installation unit of the mount bracket is adapted to be removed from the post. a fixing frame having a side wall, an end wall, and two protrusions (28a, 28b) respectively extending from a top side and a bottom side of the sidewall, the two protrusions (28a, 28b) and the side wall defining a first path, the side wall having a recess and defining a second path; an installation unit fixed to the end wall of the fixing frame; a movable member having a first board and a second board, the first board inserted into the first path of the fixing frame, the first board having a contact portion and a support frame, the support frame inserted into the second path of the fixing frame and the contact portion located adjacent to the second board, the support frame having an engaging hole, the second board having a plurality of holes which are located corresponding to the installation unit; a positioning member having a fixing portion, a resilient arm, an activation portion and an engaging portion, the fixing portion fixed to the side wall of the fixing frame, the resilient arm connected between the fixing portion and the activation portion, the activation portion extending an angle from an end of the resilient arm, the engaging portion located on the resilient arm and located corresponding to the engaging hole of the movable member; a release member movably connected to the first board of the movable member and having a push block which is located corresponding to the activation portion of the positioning member; and when assembled, the contact portion of the movable member and the second board are adapted to contact the inside and outside of the post of the rack, the installation unit is located corresponding to the holes of the post, the fixing frame is pushed toward the post to insert the installation unit into the holes of the post, only the engaging portion of the positioning member is engaged with the engaging hole of the movable member to connect the movable member to the fixing frame, and when pushing the release member, the push block of the release member contacts the activation portion of the positioning member, the resilient arm of the positioning member is lifted relative to the movable member, the engaging portion of the positioning member is disengaged from the engaging hole of the movable member, the movable member is movable relative to the fixing frame, the installation unit of the mount bracket is adapted to be removed from the post.