Surface stoichiometry of GaSb during molecular beam epitaxy is studied b using the reflection high-energy electron diffraction technique. This study has shown a desorption energy of 1.47 eV for excessively absorbed Sb atoms on the Sb-stabilized surface. It is also shown that the Ga-stabilized surface easily dissociates Ga atoms from the Sb sublayer to aggregate fine droplets. The activation energy is found to be 1.76 eV for the Ga droplet formation.