We have performed the frequency dependence millimeter wave ESR measurements on Et2Me2P[Pd(dmit)(2)](2) single crystals at 4.2 K. Antiferromagnetic resonance (AFMR) was observed for B//a and c. The hard axis is determined to be a axis by AFMR mode analyses. This result will be discussed in connection with the X- and Q-band ESR results at low temperature. We will also discuss about the magnetic anisotropy of the system and it turned out that this salt is the antiferromagnet with the easy axis type anisotropy.