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This experiment was conducted at the Research farm of the faculty of Agriculture, University of Tehran during 1995 in order to study the effects of diffrent rates of nitrogen on corn - soybean intercropping.The exprimental design was a split- plot with three replications. The main-plots were the rates of nitrogen (0,100,200, and 300, kg(ha)’). Each main plot was sub-divided into five sub-plots to accommodate the pure stands and intercrop (S1=100 % Corn, S2= 100 soybean , S3= 50 % corn +50 % soybean , S4= 75 % corn ± 25 % soybean , S5= 25 % corn + 75 % soybean). A” Replacement Series Technique “was employed to form the iutercrops.The results indicated that increasing the level of nitrogen up to 200 (kg ha’) increased grain yield number. of grain per ear, dry matter (DM) and leaf area index (LAI) of corn and grain yeild , pod number per plant , grain number per pod, dry matter (DM) and leaf area index (LAI) of soybean significantly. However, spatial arrengment only effected the number of grains per corn ear and pod number per plant ,DM and LAI of soybean. Maximum number of grains per ear was obtianed in pure stand of corn and maximum pod number per plant , DM, and LAI of soybean was achieved in S5 (25%corn + 75 % soybean).CGR,RGR, and NAR of both plants followed the normal pattern, and were higher in 200 kg nitrogen per hectare. Calculated LER showed that the maximum LER was obtained in applying 200 kg nitrogen per hectare and spatial arrengment of S5, that was 2.53. Under these conditions intercrop had advantage of 153 % over the pure stands.