This paper focuses on the role of home country's birth rates in shaping immigrants' fertility. We use the German Socio-Economic Panel (SOEP) to study completed fertility of first generation immigrants who arrived from different countries and at different times. We find that women from countries where the aggregate birth rate is high tend to have significantly more children than women from countries with low birth rates. This relationship is attenuated by selection operating towards destination country. In addition, the fertility rates of source countries explain a large proportion of fertility differentials between immigrants and German natives. The results suggest that home country's culture affects immigrants' long-run outcomes and therefore favor the socialization hypothesis.