The aim of this study was to investigate the expressions of type II collagen and aggrecan mRNA in the growing condylar and disc of the rabbit craniomandibular joint (CMJ) using in situ hybridization. 48 rabbits from newborn to 120 days after birth were divided into 8 groups. In the newborn, the morphology of the posterior band and the bilaminar zone were similar, composed with mesenchymal cells and capillaries. After weaning, the mastication loading induced the differentiation of mesenchymal cells, which accompanied with structural differentiation between the posterior band and bilaminar zone. Aggrecan first appeared in the posterior band of disc at 30 days of postnatal development, when the rabbits began to masticate solid food. Type II collagen emerged in the disc at the age of 45 days. Both genes co-expressed in the deeper half of proliferative layer, the whole hypertrophy layer and the mineralized layer of condylar cartilage, increasing the stain intensity associated with the development of ages. It was concluded that the coexpression of aggrecan and type II collagen is to represent the maturation of chondrocytes differentiation in disc and condyle, which is the foundation of biomechanical characteristic of CMJ to resist the functional stimuli.