This research has been done for studying the effect of split application of Nitrogen fertilizer on growth indexes and yield of three hybrids of grain corn in Shahrood. A split plot experiment based on randomized complete block design with four replications was carried out in 2007. Three hybrids of corn (double cross 370, single cross 447, single cross 499) were placed in main plots and split application of nitrogen which was containing the six treatments (N1: 45 Kg Nitrogen/ha in planting time, 135Kg Nitrogen/ha in flowering time, N2: 90 Kg Nitrogen/ha in planting time, 90 Kg Nitrogen/ha in flowering time, N3: 135 Kg Nitrogen/ha in planting time, 45 Kg Nitrogen/ha in flowering time, N4: 45 Kg Nitrogen/ha in planting time, 67.5 Kg Nitrogen/ha three weeks before flowering, 67.5 Kg Nitrogen/ha three weeks later flowering, N5: 90 Kg Nitrogen/ha in planting time, 45 Kg Nitrogen/ha three weeks before flowering, 45 Kg Nitrogen/ha three weeks later flowering, N6: 135 Kg Nitrogen/ha in planting time, 22.5 Kg Nitrogen/ha three weeks before flowering, 22.5 Kg Nitrogen/ha three weeks later flowering) were placed in sub plots. In total, in each treatment 180 Kg/ha pure Nitrogen (392 Kg/ha Nitrogen) has been used. Results show that hybrid of 499 and fourth fertilizer treatment has had the highest total dry matter (TDM). Also, the highest leaf area index (LAI) has been shown in hybrid of 447 and fourth fertilizer treatment and the highest crop growth rate (CGR) and net assimilation rate have been achieved in sixth fertilizer treatment. In third fertilizer treatment the highest relative growth rate (RGR) has been obtained. Analyses of data variance showed that hybrids had significant effect on grain yield in hectare, number of ear in bush and ear weight. Fertilizer treatments had significant effect on grain yield in hectare, number of ear in bush, ear weight, biological yield and weight of 100 grains. Also the effect of interaction of hybrid-fertilizer treatments has significant effect on grain yield in hectare, number of ear in bush and ear weight. The highest grain yield in hectare was shown in hybrid of 499 with first and forth fertilizer treatments. Based on obtained results, the highest number of single-ear bushes has been shown in hybrid of 499. The highest weight of ear was achieved in hybrid of 499 with first fertilizer treatment. Finally, in total, application of hybrid of 499 with first and forth fertilizer treatments is ...