湮灭（英语：annihilation）是指当物质和它的反物质相遇时，会发生完全的物质-能量转换，产生能量（如以光子的形式）的过程，又称互毁、相消、对消灭。

其遵守爱因斯坦的质能关系式E=mc。其中E为湮灭产生能量，m为参与的正物质和反物质湮灭前总静止质量，c为光速≈3x10米/秒。举例来说，二分之一克反物质湮灭所产生的能量大约与广岛市原子弹爆炸所产生的能量相当（即是一克反物质湮灭所产生的能量约为20-30千吨TNT当量，或者是大约200亿千卡）。

一个正电子和一个电子碰撞后湮灭，通过光子的形式释放能量，这一过程仍然满足电荷守恒定律，因为湮灭前后电荷总和保持为零。

Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil (nothing). A literal translation is "to make into nothing".

In physics, the word is used to denote the process that occurs when a subatomic particle collides with its respective antiparticle, such as an electron colliding with a positron. Energy and momentum are conserved, and the annihilated particles are replaced by photons, electromagnetic wave quanta with zero rest mass. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of the original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed. When a particle and its antiparticle collide, their energy is converted into a force carrier particle, such as a gluon, W/Z force carrier particle, or a photon. These particles are afterwards transformed into other particles.