A bicycle cable assembly mainly includes an external protection tube composed of several hollow sleeves hooking together. Hooks and engaging edges of the sleeves hook together so that the external protection tube is formed and can be properly adjusted according to a length of a cable and a special position by increasing or decreasing the number of sleeves. Also, the hook hooking the engaging edge can prevent the external protection tube from being arbitrarily disassembled by others. Also, it is possible to effectively prevent an inner protection tube from exposing to the outside and thus being damaged. Thus, a protection layer can be indirectly added to the bicycle cable assembly.