Effects of different levels of farmyard manure and P and N fertilizers on growth and yield of seed potato, Peshendy variety, were studied. Growing season in Zanjan area was on date 1376-1377. This experiment was conducted as a split plot design in randomized complete blocks design with four replications. In this study farmyard manure was applied at three levels (0,25 and 50 ton ha-1), phosphorus at four levels (0, 80, 160 and 240 kg P2O5 ha-1), and nitrogen at four levels (0,80, 160 and 240 kg N ha-1) The results showed that levels of farmyard manure increased plant height, and also percent of medium and small size tubers per hectare. The higher levels of farmyard manure mcreased density of tuber. The large and medium size tubers in N rates is compared with treatment of 80 kg plots were higher. Generally N fertilizer rate increased the medium size of tuber in total yield of crops. The higher levels of farmyard manure, P and N reduced the amounts of dry meter in tuber.