A self-closing mechanism for use in a slide rail assembly, the self-closing mechanism comprising: a housing comprising a first edge, a second edge deflecting from the first edge, and an engaging portion located at the second edge; an elastic member located in the housing; and a movable member movably connected to the housing, the movable member comprising a first projection pressed against the elastic member, wherein the movable member is movable along the first edge and the second edge of the housing in response to elastic energy provided by the elastic member and is engaged with the engaging portion when moved to the second edge of the housing, wherein the movable member further comprises a second projection, the second projection being movable along the first edge of the housing; the movable member has a first side and a second side opposite the first side, the first projection and the second projection of the movable member being located on the first side; the movable member can be moved from the first edge to the second edge of the housing and enter into engagement with the engaging portion via the second projection; the housing has a longitudinal portion and a transverse portion connected to the longitudinal portion, the first edge of the housing being substantially parallel to the longitudinal portion, the elastic member being located in the longitudinal portion, the second projection of the movable member corresponding to the transverse portion; and the self-closing mechanism further comprises an actuating portion connected to the second side of the movable member, and wherein the housing further comprises a channel filled with a cushioning medium; an auxiliary member has a sliding portion corresponding to the channel, a first vertical wall, and a second vertical wall opposite the first vertical wall; characterized in that the second projection of the movable member is located between the first vertical wall and the second vertical wall of the auxiliary member. a housing comprising a first edge, a second edge deflecting from the first edge, and an engaging portion located at the second edge; an elastic member located in the housing; and a movable member movably connected to the housing, the movable member comprising a first projection pressed against the elastic member, wherein the movable member is movable along the first edge and the second edge of the housing in response to elastic energy provided by the elastic member and is engaged with the engaging portion when moved to the second edge of the housing, wherein the movable member further comprises a second projection, the second projection being movable along the first edge of the housing; the movable member has a first side and a second side opposite the first side, the first projection and the second projection of the movable member being located on the first side; the movable member can be moved from the first edge to the second edge of the housing and enter into engagement with the engaging portion via the second projection; the housing has a longitudinal portion and a transverse portion connected to the longitudinal portion, the first edge of the housing being substantially parallel to the longitudinal portion, the elastic member being located in the longitudinal portion, the second projection of the movable member corresponding to the transverse portion; and the self-closing mechanism further comprises an actuating portion connected to the second side of the movable member, and wherein the housing further comprises a channel filled with a cushioning medium; an auxiliary member has a sliding portion corresponding to the channel, a first vertical wall, and a second vertical wall opposite the first vertical wall; characterized in that the second projection of the movable member is located between the first vertical wall and the second vertical wall of the auxiliary member.