Abstract: To study, the growth of different shoot parts of two potato cultivars under the effects of different levels of N fertilizer, a split-plot experiment was conducted based on Completely Randomized Block Design (CRBD) with four replications in Ardabil agriculture research station in 2007. Cultivars included Agria and Satina and N fertilizer levels included control, 80, 160 and 200 kg N ha-1. Results showed that Agria was significantly superior in all traits except stem length. The effect of N on all traits was significant. As N level increased, auxiliary branch number and plant height increased. The maximum stem and leaf biomass and leaf number was achieved in 160 kg N ha-1 treatment and the highest main stem number was achieved in 80 kg N ha-1 treatment. The yield difference among 80, 160 and 200 kg N ha-1 was insignificant. Over time auxiliary (not main) branch number, plant height, stem dry weight and tuber yield increased. Leaf number and leaf biomass declined after 94 DAP (Days After Planting). Generally, potato is a crop that strongly affected by nitrogen rates. But the effect of nitrogen on aboveground was more violent than tubers. Therefore, a range of 80-160 kg N ha-1 is recommended.