Objective: To elucidate the expression and significance of cell cycle-associated proteins in chondrosarcoma of the jaws. Methods: CDK4, p27, and E2F-1 expression were examined in chondrosarcoma and osteochondroma of the jaws by immunohistochemical ABC method. Results: CDK4, p27, and E2F-1 were positive in 60% (12 of 20), 25% (5 of 20), and 65% (13 of 20), respectively, in chondrosarcoma of the jaws. There was no significant difference in the expression of CDK4, p27, and E2F-1 among histological grade of the chondrosarcoma (P>0.05). In osteochondroma of the jaws, CDK4 and E2F-1 showed an equal positivity of 12.5% (1 of 8), whereas p27 was positive in 87.5% (7 of 8). The positive rate of CDK4, p27, and E2F-1 was significant between chondrosarcoma and osteochondroma of the jaws (P<0.05). Conclusion: These data show that cell cycle regulatory proteins are altered in chondrosarcoma of the jaws. CDK4 and E2F-1 are over-expressed and p27 is under-expressed in chondrosarcoma of the jaws.