The nanocomposites (denoted "CII-Au") of porcine type II collagen (CII) with 0.05, 0.1, 0.5, 1, or 2.5% (wt/wt) Au nanoparticles ( approximately 5 nm) were fabricated for potential use in cartilage tissue engineering. Au formed clusters on the surface of all nanocomposites and appeared to distribute along the collagen fibrils inside the matrix. The addition of Au at low concentrations (< or =0.5%) increased the modulus and viscosity, as well as the free radical-scavenging ability. These effects decreased at higher concentrations of Au. The chondrocytes on CII-Au became spindle-like with lamellipodia formation. Cell proliferation on CII-Au 0.1% was promoted. Nitric oxide (NO) in the culture medium was reduced by CII-Au 0.05% and CII-Au 0.1%. Type I collagen, aggrecan, and Sox 9 gene expressions increased with an increased Au content, but slightly decreased at 2.5% Au. There was no significant difference in the CII gene expression. The cellular uptake of Au was observed but less than that which occurred when 10 ppm of Au was added in culture medium. Chondrocytes cultured with < or =10 ppm of Au nanoparticles showed neither cytotoxicity nor change in gene expression. Au at an appropriate amount could be well dispersed in CII, and enhanced the material modulus, antioxidant effect, as well as the chondrocyte growth and matrix production.