Presented is a study of uncompensated magnetization in antiferromagnets performed by SQUID and VSM magnetometry, and polarized neutron reflectometry. This uncompensated magnetization is observed and studied as a function of temperature and cooling conditions. Uncompensated magnetization is found close to the top surface of the antiferromagnet (interface with the ferromagnet) and also in the “bulk” of the antiferromagnetic film. It has been established that this uncompensated magnetization plays crucial role in exchange bias. To understand the origin of uncompensated magnetization, ab initio calculations are performed.