Characteristics of the upper and lower molar series in terms of crown cusp areas were described for Pan and Gorilla, and then affinities between these African apes and living and fossil hominids were discussed. The conclusions are summarized as follows. 1) intraspecific comparisons indicate that the area variability within the distal cusps tends to be larger than those within the mesial cusps. 2) the relative cusp areas of M_1 display a marked interspecific variation among the apes and hominids compared. 3) the interspecific variation of M_1 can not be explained from allometric or phylogenetic factors, but may be affected by environmental ones such as diet. 4) as for Pan's M_1,the close resemblance to its M_2 implies that Pan's M_1 has a more primitive pattern of the relative cusp areas than other hominoids's M_1.