Abstract: The effects of different nitrogen levels (N0 = control, N1 = 101 Kg ha–1 and N2 = 202 kg ha–1) on net photosynthesis (PN), stomatal conductance (SC), transpiration rate (TR), water use efficiency (WUE) and leaf chlorophyll (LC, SPAD value) were studied in field grown potatoes (Solanurn tuberosum L. cvs. May Queen and Dejima). PN increased by the application of N to a smaller extent over control. In all cases, trend of PN initially increased and reached the peak at the time of tuber initiation and then gradually decreased. SC also increased in the N treated plant. The TR increased sequentially as fertilizer N level increased and WUE also increased by N treatment. Nitrogen fertilizer effect was more pronounced in case of LC. Higher N treated plant showed the higher levels of LC at all stages of growth. PN also showed highly significant positive correlation with SC, TR, WUE and LC. Between the cultivar PN, SC, TR and LC is comparatively higher in Dejima than May Queen. In conclusion, PN increased through the increase of SC resulted by the increase of TR, WUE and substantially increased the LC.