“外部性”是新制度经济学理论中探讨的一个重要问题。为了解决这个问题,新制度经济学家提出了“科斯定理”。什么是“外部性”,为什么外部性问题既是一个经济问题又是一个伦理问题,从经济伦理的角度怎么看待“科斯定理”?这是本文所要讨论的问题。 “Externality” is an important issue discussed in the new institutional economics theory. In order to solve this problem, the new institutional economists put forward the “Coase Theorem.” What is “externality” and why the externality issue is not only an economic issue but also an ethical issue. How to treat the “Coase Theorem” from the perspective of economic ethics? This is the issue to be discussed in this article.