电子偶素或称正电子素(positronium)是一个电子与一个正电子组成的亚稳定的束缚态(e-e+(ee)，化学符号是Ps。最早由麻省理工学院物理学家Martin Deutsch在1951年发现。

由于电子和正电子最终会湮灭产生光子，电子偶素的半衰期是很短的。根据电子与正电子自旋状态的不同，电子偶素主要分为两种。单态(S₀，自旋相反，总自旋为0)即仲电子偶素(para-positronium，简记为p-Ps)，三重态(S₁，自旋同向,总自旋为1)即正电子偶素(ortho-positronium，简记为o-Ps)。在真空中，单态的电子偶素半衰期为125ps，之后湮灭产生两个光子(511keV)；三重态电子偶素半衰期为142ns，湮灭产生三个光子，有时会产生多个光子。光子总能量为1022keV，即电子和正电子的总质量。

This article is about the exotic atom. For the hydrogen isotope, see Protium.

Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states. The orbit and energy levels of the two particles are similar to that of the hydrogen atom (which is a bound state of a proton and an electron). However, because of the reduced mass, the frequencies of the spectral lines are less than half of the corresponding hydrogen lines.