Abstract: Due to the relatively high and stable yield， and high tolerance to drought， sweet potato is suitable to be cultivated in the newly reclaimed mountain land. In order to determine the suitable application amount of N\|fertilizer， three sweet potato cultivars and two N\|fertilizer application levels were used to study the influence on photosynthetic characteristics of sweet potato leaves. The results showed that the difference of specific leaf weight was not significant between two N\|fertilizer levels. The contents of chlorophyll b， chlorophyll （a+b） and leaf nitrogen were dramatically increased under high N level. The related parameters of light response curve， such as the initial quantum efficiency （α）， maximum photosynthetic rate （Pnmax）， saturation light intensity （PARsat）， light compensation point （Ic） and dark respiration rate （Rn） showed no significant differences （P＞005） in general. And， the relevant parameter curve in response to CO2， namely， the maximum rate of carboxylation （Amax） and CO2 compensation point （Γ）， also showed no significant changes （P＞005）. But， the initial carboxylation efficiency and saturation intercellular CO2 concentration varied significantly （P<005）. In general， photosynthetic characteristics of sweet potato leaves were not significantly influenced by N application level. Thus， N\|fertilizer amount was suggested to be appropriately reduced for sweet potato production.

Key words: sweet potato, N\, fertilizer, light intensity, CO2, photosynthesis