A ratchet wrench (10) includes a head (12) having a compartment (121) rotatably receiving a drive member (12). An annular groove (126) is formed in an inner periphery of the compartment (121) and in communication with a recess (13) formed in a side (F2) of the head (12). A flange (2121) is formed on an outer periphery of the drive member (21) and intermediate a toothed portion (213) of the drive member (21) and an annular groove (214) formed in the outer periphery of the drive member (21). A flange (2121) is formed on the outer periphery of the drive member (21) and includes an inner end face (2122) facing a bottom face (133) of the recess (13). A C-clip (24) is received in the annular grooves (126, 214) and has two clamping portions (241) received in the recess (13). A dustproof cap (30) engaged in the recess (13) and located intermediate a bottom face (133) and the recess (13) and the inner end face (2122) of the flange (2121). The dustproof cap (30) covers the clamping portions (241) of the C-clip (24) and covers and seals the recess (13).