The critical behavior of small magnetic particles of the real antiferromagnetCr2O3is investigated by the Monte Carlo method. The critical exponents &agr;,&bgr;,&ggr; and the corresponding critical amplitudes for particles containing from 286 to 2502 spins are calculated. It is found that the presence of superficial spins extends the temperature range with the Heisenberg critical behavior and displaces the crossover temperature to the critical point. ©1998 American Institute of Physics.