This study aimed to investigate how nitrogen deficiency affects PSII primary photochemistry and PSII electron transport in lupine plants grown under natural illumination. Plants with low nitrogen expressed considerably lower values in chlorophyll content, maximal CO₂ assimilation capacity and the apparent quantum yield of photosynthesis than plants with high nitrogen. Plants with low nitrogen expressed a small decrease in maximal photochemical efficiency of PSII, which was due to a decrease in the maximal fluorescence. Compared to the plants with high nitrogen, the plants with low nitrogen exhibited lower average in both quantum yield of PSII electron transport and the efficiency of excitation energy capture by open PSII reaction centers at all photosynthetic flux density (PFD) and the differences were more apparent at moderate and high PFD than at low PFD. The maximum photochemical efficiency of PSII was declined when plants with low nitrogen and those with high nitrogen were photoinactiavted. A greater decrease of photochemical quenching coefficient was observed in both types of plants during photoinhibition. In contrast, nonphotochemical quenching coefficient increased with increasing the time of photoinhibition but a greater increase occurred in plants with high nitrogen. Plants with low nitrogen expressed 25 % increase in the percentage inactive PSII centers. Thus, the results in the present investigation implicate that increase susceptibility could be associated with the greater accumulation of inactivated PSII reaction centers, less capability for dissipation of excess excitation energy, as well as the higher fraction of reduction state of primary electron acceptor of PSII.