中子毒物（英语：Neutron poison）是一种具有大中子吸收截面的物质，由于会对连锁反应造成负面影响，而被称为「毒物」，常应用于反应堆物理计算中。在反应堆中，我们尽可能希望中子由可裂变物质吸收，使之发生核分裂。然而，一些物质具有强烈的中子捕获现象，会导致降低反应器运转的反应性。有些毒物会在反应器运转过程中吸收中子而消耗掉，但有些则保持不变。

中子被短半衰期的核分裂产物吸收称为「反应堆中毒」；中子被长半衰期或稳定的核分裂产物吸收称为「反应器结渣」。

A neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section, in applications such as nuclear reactors. In such applications, absorbing neutrons is normally an undesirable effect. However neutron-absorbing materials, also called poisons, are intentionally inserted into some types of reactors in order to lower the high reactivity of their initial fresh fuel load. Some of these poisons deplete as they absorb neutrons during reactor operation, while others remain relatively constant.