The effect of temperature and size on the exchange bias field of a hysteresis loop was studied based on the model of two-phase core/shell nanoparticles. Using the random interaction field method, the temperature dependence of the interfacial exchange interaction constant was estimated. It is shown that with increasing temperature, the field of exchange bias as well as the constant of interphase exchange interaction fall exponentially. An increase in the inverse size of nanoparticles leads to a linear growth of the exchange bias field.