We analyze the impact of the diffusion of Protestantism on agricultural development in China using a dataset at the prefecture level. Our findings indicate a significantly positive effect of Protestantism on Chinese agricultural productivity, implying that Protestant missionaries introduced valuable Western knowledge that encouraged agricultural development. However, this effect is weakened by the use of organic fertilizers, small plot sizes, and rice cultivation, highlighting that the effectiveness of this “useful” knowledge differs in an environment that greatly contrasts with Europe and the US. These results align with the “inappropriate technology hypothesis,” which suggests that customizing technology to local conditions hinders its diffusion and productivity benefits in other contexts.