This study was carried out in test ground of Uludag University Vocational School of Technical Sciences. The test used Randomized Block Design with 3 replications and Seydisehir forage oat cultivar. 4 different doses of nitrogen (0, 5, 10, 15 kg N da-1) and ammonium sulfate fertilizer containing 21% N and ammonium nitrate fertilizer containing 26% N were used. Plant specimens were collected in 3 replications in milk stage (MS), dough stage (DS) and physiological stages (PS) of the plant. It was found that the lowest total dry weight (DW) was obtained in PS, while the highest total DW was obtained in DS. In all organs excluding the grains, Dry matter (DM) amount was found to be the highest in MS; however, it decreased in next stages of maturity. It was found that applied nitrogen doses had a significant effect on grains, flag leaf and other leaves on DM production. On the other hand, nitrogen contents decreased as the maturity periods progressed in above ground organs excluding the grains.