Type I and type II collagens are considered the major collagens of bone and cartilage respectively. Monitoring the patterns of those gene and protein expressions during development will provide a basis for the understanding of the normal and abnormal growths. This study was undertaken to investigate the expression of collagen genes and proteins involved in the developing human mandible. Fifty embryos and fetuses were studied with Alcian blue-PAS, Masson´s Trichrome, reverse transcription polymerase chain reaction (RT-PCR), Western blot analysis, and Southern blot analysis. Our results showed that pro-α1(II) collagen gene expression begins in the 5th week. Type II collagen is synthesized in mesenchymal cells in advance of overt chondrogenesis. The gene expression for type II collagen was highest during the appearance of Meckel´s cartilage. There was a switch in collagen protein expression from type I to type II during the appearance stage of Meckel´s cartilage. The distribution of the mRNA for type II collagen corresponded well with the pattern of type II collagen protein. The endochondral ossification was observed where there was direct replacement of cartilage by bone.