保守扩展是逻辑中的一个概念。一个知识库K'是K的扩展，如果K是K'的一个子集；K'是K的保守扩展，如果对所有只用K中的名字构造的命题, K' 当且仅当 K。换句话说，保守扩展不会改变原有的知识库的结构。保守扩展在许多领域都有应用，如模块化本体和敏感知识的保护。

在逻辑和推导机制中，I和J分别是一个解释(Interpretation),如果J是I的保守扩展，必须满足以下条件:

那幺我们说J是I的保守扩展。

In mathematical logic, a conservative extension is a subtheory of a theory which is often convenient for proving theorems, but proves no new theorems about the language of the original theory.

More formally stated, a theory is a (proof theoretic) conservative extension of a theory if the language of extends the language of ; that is, every theorem of is a theorem of , and any theorem of in the language of is already a theorem of .