The Br2-methanol system has been found to give good results for chemical polishing etching of GaSb except for the {111}Ga plane. The etching rates for {100}, {111}A, and {111}B of n-type GaSb have been studied as a function rate vs. Br2 concentration. By comparing the activation energies for the above etching process and the temperature dependence of viscosity of liquid methanol, the above etching process is shown to be a diffusion-controlled reaction. The etching of the {111}A plane of GaSb, however, is preferential with a reaction-limited etching rate. Further experiments show that the etching rates for {100} and {111}B GaSb are similar to these for {100}GaAs, InAs, and InP as expected for diffusion-limited processes.