It is important to elucidate the effects of carbon nanotubes on cell functions for their biomedical applications. In this study, the effect of single-walled carbon nanotubes (SWCNTs) on the mechanical property of chondrocytes was investigated by atomic force microscopy. Chondrocytes were cultured in medium containing SWCNTs and showed an increase uptake of SWCNTs with culture time. The mechanical property of chondrocytes cultured with or without SWCNTs was measured at an indentation depth of 200 nm and 500 nm. The chondrocytes cultured with SWCNTs showed higher Young's modulus than that of cells cultured without SWCNTs at both indentation depths. The increase became significant after culture for more than 3 hours. Indentation at 500 nm depth magnified the change of Young's modulus compared to that monitored at 200 nm indentation depth. The results indicated uptake of SWCNTs increased the Young's modulus of chondrocytes.