As one of the most fundamental aspects of nanomaterials, the crystal orientation in semiconductor nanowires (NWs) profoundly reshapes their properties, e.g. surface chemistry, optical response and electrical transport. Among the various semiconductor NWs, free-standing InSb NWs hold promise for making high speed and low power vertically integrated nanowire transistors, chemical/biological sensors, etc. However, the difficulty of controlling the crystal orientation and growing well-defined single crystal NWs is limiting the applications. In this work, (111)-orientated vertical InSb NWs are achieved on GaAs substrate through a hetero-epitaxy process by metal-organic chemical vapor deposition (MOCVD). The effects of growth parameters such as temperature, rV/III ratio on the InSb NWs have been studied systematically. In addition, a substrate caused NW morphology variation is observed and explained with a phenomenological model. This work is supported by Sun Yat-Sen University Special Project for Exploration in the Field of National Defense Scientific (76120-31143411).