Fourier transform infrared imaging (FTIRI) was used to examine the depth-dependent content variations of macromolecular components, collagen and proteoglycan (PG), in osteoarthritic and healthy cartilages. Dried 6 μm thick sections of canine knee cartilages were imaged at 6.25 μm pixel-size in FTIRI. By analyzing the infrared (IR) images and spectra, the depth dependence of characteristic band (sugar) intensity of PG show obvious difference between the cartilage sections of (OA) and health. The result confirms that PG content decreases in the osteoarthritic cartilage. However, no clear change occurs to collagen, suggesting that the OA influences little on the collagen content at early stage of OA. This observation will be helpful to further understand PG loss associated with pathological conditions in OA, and demonstrates that FTIRI has the potential to become an important analytical tool to identify early clinical signs of tissue degradation, such as PG loss even collagen disruption.