In this paper, we report the effect of Ti underlayer and in situ substrate temperature on the structure, microstructure, magnetic and magnetostrictive properties of Fe-Ga thin films grown on Si 100. Films deposited at room temperature were found to form in single phase with disordered A2 type structure. Upon increase in substrate temperature, presence of ordered L12 phase co-existing with A2 phase has been observed. However, Ti underlayer was found to be less effective in promoting the ordering of L12 phase. Nevertheless, films grown at higher substrate temperature with Ti underlayer was found to show a considerable increase in magnetostriction. The change in the magnetostriction was explained based on the complex interplay between the structural ordering and magnetic microstructures present in the films. This study suggests that growth of Fe-Ga thin films with Ti underlayer coupled with enhanced substrate temperature is beneficial for achieving large magnetostriction. © 2019 IOP Publishing Ltd.