反铁磁性（英语：antiferromagnetism）是磁性材料的磁学性质的一种。在这种材料中，相邻电子自旋呈相反方向排列，其磁化率因而接近于零。1932年由Louis Néel首次发现。例如，铬、锰、轻镧系元素等等，都具有反铁磁性。

当温度大于奈尔温度时，磁化率与温度的理论关系式为

做实验得到的经验关系式为

其中，是依物质而定的常数，与差别很大。

理论而言，当温度小于奈尔温度时，可以分成两种状况：

In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. Generally, antiferromagnetic order may exist at sufficiently low temperatures, vanishing at and above a certain temperature, the Néel temperature (named after Louis Néel, who had first identified this type of magnetic ordering). Above the Néel temperature, the material is typically paramagnetic.