Tuning of the photoluminescence property of carbon nanodots is realized by surface modification through ultraviolet light irradiation. The photoluminescence of the processed carbon nanodots in the visible region is weakened while that in the ultraviolet region increases significantly. Fourier transform infrared spectroscopy and X-ray photo-electron spectroscopy reveal that the number of surface functional groups decrease significantly after ultraviolet light processing. By examining the electron donating and accepting properties, we confirm that the surface of the carbon nanodots is photoreduced by ultraviolet light, causing a decrease in the number of functional groups as well as emission in the visible region. The temporal behavior of the photoluminescence reveals that the increase of the emission in the ultraviolet region originates from the increased intrinsic state emission of the carbon nanodots.