The present study was carried out from 346 skulls of Praomys jacksoni (Muridae) captured in some forest areas of the surroundings of Kisangani city (island, right and left banks of Congo River) from 1994 to 1999). The results obtained from twenty-five skulls measurements revealed the diversity existing inside each population studied. The sexual dimorphism is favorable to males for seven measurements (GRLE, HEBA, DIA1, DIA2, INT, LNAS, and LOTE) whereas eighteen remain stable. The skulls of insular populations (Tundulu and Mbiye) are bigger than those of the forest reserves ( Masako and Yoko) for twenty measurements: GRLE, PRCO, HEBA, HEPA, DIA1, DIA2, INT, ZYPL, PAL, UPTE, UPDE, M1, BNAS, LNAS, BUL, DIN, HRZ, ROH, ROB and PCPA The skulls of Mbiye island populations are bigger than those of Tundulu island for eighteen measurements (GRLE, PRCO, HEBA, HEPA, PAF, DIA1, DIA2, ZYG, UPTE, UPDE, M1, ZYPL, BNAS, LNAS, LOTE, CHOA, DIN, PCPA). The skulls of populations from the left bank (Yoko forest reserve) are bigger than those of the right bank for six measures (GRLE, HEBA, DIA1, INT, CHOA and PAF). These results indicate that craniometrical measurements of the adult animals are stable and constitute a complementary means for identifying the species in the Praomys genus. The variations observed with certain examined characters would be the consequence of the biological phenomenon of speciation. It is thus desirable that molecular studies are carried out on these muridae in order to validate this hypothesis.