A bracket device of a slide rail assembly comprises a supporting frame, a bracket, and a fastening member. The bracket comprises a longitudinal wall and a mounting member. The longitudinal wall is connected to the supporting frame. The mounting member is adjacent to the longitudinal wall. The fastening member is pivotally connected relative to the bracket. When the fastening member is rotated in a first direction from a predetermined state, a fastening section of the fastening member moves away from the mounting member. The bracket device further comprises two blocking features arranged on a rotation path of the fastening member in a second direction. When the fastening member is in the predetermined state, the two blocking features are disposed beside two parts of the fastening member, and the blocking features prevent the fastening member from being rotated in the second direction from the predetermined state.