We characterize hydroxylapatite and collagen by Fourier transform infrared (FTIR) imaging and light microscopy in different aged rats to investigate bone formations. The proximal tibias from male rats aged between fetus and postnatal 33 weeks were embedded and sliced to make longitudinal sections. FTIR images of amide I distribution in the sections are coincident with the images of Goldner's stained-sections. FTIR images of hydroxylapatite indicate calcification of rat bones can be observed until postnatal 33 weeks at least. It is found for fetus that hypertrophic chondrocyte in perichondrium and bone collar are initially calcified and have poorly ordered hydroxylapatite crystallites.