The effects of nitrogen doping into Cu₂O thin films deposited by reactive radio-frequency magnetron sputtering were studied. It was found that nitrogen is an effective p-type dopant for Cu₂O and the hole density can be controlled from 1×10¹⁵ cm^-3 to approximately 10¹⁷ cm^-3. The acceptor level of nitrogen was estimated to be about 0.14 eV by temperature-dependent Hall effect measurements and this value roughly agrees with that obtained by the effective mass theory. No significant degradation of structural and optical properties induced by nitrogen doping were observed. The resistivity of 15.2 Ωcm was obtained for a relatively high nitrogen flow rate, which is the lowest value reported to date for Cu₂O thin films.