Copper ion irradiation at room temperature and at 573 K up to 1 dpa was conducted on vanadium doped with controlled levels of nitrogen ranging from 12 to 770 weight ppm (wppm). Micro-indentation test was performed to make a quantitative estimation of hardening of the irradiated surface layer. Microhardness of the unirradiated and as-irradiated vanadium increased with increasing nitrogen content. They showed linear relationship when nitrogen was singly varied. Irradiation hardening was independent of nitrogen content and of irradiation temperatures. This fact agrees with microstructure observations. After post-irradiation annealing at 573 K, radiation anneal hardening (RAH) was observed at the nitrogen contents of 170 wppm and above. In comparison with the previous anneal hardening experiments with cold-worked specimens, stepwise increase in the anneal hardening with nitrogen content at about 100 wppm was commonly derived for cold-worked and irradiated vanadium.