We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using compositionally graded GaAs_xSb_(1-x) buffer layers. Optimization of GaAs_xSb_(1-x) growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of GaAs_xSb_(1-x)layers are found to be 420℃ and 0.5μm,respectively. The smallest full width at half maximum value and the root mean square surface roughness of 0.67 nm over 2×2μm~2 area are achieved as a 250 nm GaSb film is grown under optimized conditions. We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using compositionally graded GaAs_xSb_ (1-x) buffer layers. Optimization of GaAs_xSb_ (1-x) growth parameters is aimed at obtaining high GaSb crystal quality and smooth GaSb surfaces. growth temperature and thickness of GaAs_xSb_ (1-x) layers are found to be 420 ° C and 0.5 μm, respectively. The smallest full width at half maximum value and the root mean square surface roughness of 0.67 nm over 2 × 2 μm ~ 2 area are achieved as a 250 nm GaSb film is grown under optimized conditions.