We investigate how social capital in both the home and host countries affects foreign direct investment in high tech firms. Difference in the social capital (trustworthiness) among provinces of the host country, China, is shown to matter in foreign companies’ choice of location, ownership type, and investment in R&D. We find that the provinces in China characterized by high levels of social capital attract more foreign investment. We also find that the likelihood of foreign investors establishing joint ventures with local partners increases with the level of social capital prevailing in that area. Foreign high tech firms conduct more R&D investment and hire more R&D personnel in high-social-capital provinces. Moreover, foreign-owned firms located in high-socialcapital areas keep improving their intensity of R&D investments over time. By contrast, in lowsocial- capital areas, foreign high tech firms do not improve and actually diminish their R&D intensity over time. We further show that the social capital in the country of origin (the home country) of a foreign company also affects its investment decisions in China. Cultural difference between the home country and the host country magnifies the foreign company’s weighing of the regional social capital difference in the host country; foreign companies from higher uncertainty avoidance home country prefer to invest in regions with higher social capital in the host country; on the other hand, kinship decreases the need to deal with strangers, and thus reduces the reliance on the provincial social capital.