An experimental study was performed on Marangoni convection due to temperature and concentration gradients on a free surface during InSb crystal growth. InSb was grown from InxSb1-x melt one directionally in a carbon rectangular crucible. The velocities on the free surface were measured in two cases: one is that the directions of the driving forces for thermal and solutal convection are the same (acceleration case), and the other is that the directions of the driving forces are opposite (deceleration case). In the deceleration case, the flow direction on the free surface is from the crystal-melt interface to the bulk of the melt. This flow direction is opposite to the flow direction without consideration of solutal convection.