In order to study and determine the suitable rate of N fertilizer and time of sidedressing and its relation with chlorophyll content of the tobacco leaf, a factorial experiment was conducted in Randomized Complete Block designs with 3 replications and 12 treatments. Treatments were: Factor A: time of sidedressing for two variants, t¹ three weeks after transplanting and t², five weeks after transplanting. Factor B: the rates of N fertilizer for 6 levels: 0, 15, 30, 45, 60, 75 kgN/ha. The flue-cured cultivar grown was Coker 347. Two thirds of the N fertilizer were used as basic at transplanting time and 1/3 was used as sidedressing. Readings of leaf chlorophyll content were done on various spots of low, middle and upper leaves. For this purpose a chlorophyll meter SPAD 502 was used. Readings were done before sidedressing and at different stages of plant growth. Observations were as follows: cured yield, the value of the yield/ha, average value of one kg cured leaf, sugar, nicotine, chlorine, nitrogen and chlorophyll contents of leaves. There were no significant differences between treatments for the following traits in relation with factor A: cured yield, value of cured leaves/ha, average value of one kg tobacco, chlorophyll content and N content. But for the various levels of N fertilizer (factor B) there were significant differences (at 1% threshold for all traits except value of one kg cured leaf at 5% threshold) among treatments. Comparison of treatments means for factor B levels by Duncan's method showed that the highest cured yield and the value of one kg cured leaf were obtained with treatment 45 kg/ha N, the highest chlorophyll content was obtained with treatment 75 kg/ha N, and treatments 60 and 75 kg/ha N resulted in the highest leaf N content. The experiment showed that by increasing N fertilizer, chlorophyll content and leaf N content increased, and the value of one kg cured leaf decreased. The related regression equation showed that the relation between N and chlorophyll is in linear form and second degree. Also, as the best treatment is 45 kg/ha N, thus by considering chlorophyll content of the leaves before sidedressing of N fertilizer, we can estimate the plant need to N sidedressing by the orthogonal polynomial.