The mechanisms of the ME effect of Cr2O3were experimentally determined at 4.2 K. For this purpose, ME susceptibility was measured statically by SQUID from 1.6 to 270 K and the electric shift of AFMR was observed at 4.2 K by an ac modulation method. The former experiment gave &agr;∥(4.2 K) =−0.8, &agr;∥(255 K) =15.3 and &agr;⊥(4.2 K) =−4.7 in 10−4cgs unit. The latter gave a frequency shift of −1.02×10−6cm−1at E=1 cgs in the case of both E&drarr; and H&drarr; parallel to the c axis. From these experiments, &dgr;g=−1.05×10−8and &dgr;D=−3.3×10−6cm−1were deduced for E=1 cgs along the c axis. This value is not only too small but of the wrong sign to explain the sign and the magnitude of &agr;∥at higher temperatures. &agr;⊥at 4.2 K seems too large to be interpreted by the tilting of the easy axis of spins and the role of other mechanisms such as the appearance of a Dzyaloshinski interaction is suggested.