In this paper，the firm’s Ｒ＆D decision is separated into two stages: whether to invest and how much to invest． The influences of government subsidy on Ｒ＆D decisions in firms with different ownership structures are discussed． Theoretically，a two-stage model of firms’Ｒ＆D decisions is constructed to investi-gate the mechanism of subsidy on Ｒ＆D investment． Empirically，using the sample data of Chinese industrial firms，the Heckman two-step method and two-stage least square are used to deal with sample selective bias and endogeneity respectively． The sub-samples of state-owned，private and foreign firms are also tested separately．The results show that under different ownership structures，the influences of government subsidy on firms’ Ｒ＆D decisions are different． To undertake social responsibility，the state-owned firms usually have a high probability of engaging in Ｒ＆D activities under preferential policies． However，because of special property re-lations and soft budget constraints，the state-owned firms lack incentives to increase Ｒ＆D investments． For the well-organized foreign firms and less competitive private firms，the incentive effects of government subsidy on Ｒ＆D are more obvious．