Two field experiments were conducted at ElSerw Agricultural Research Station, Damietta Governorate during the two seasons (200land 2002) to investigate the influence of farmyard manure, mineral and bio nitrogen fertilizer and their interactions on cotton seed yield, its components and nutrients contents of cotton leaves. Split split plot design with four replicates was used. The most important results could be summarized as follows. Adding 2Om3Ifed. of farmyard manure induced significant increases ¡n boll weight, seed index, seed cotton yield, oil content, oil yield and lint yield. Also N,P and K contents of leaves were significantly increased ¡n both seasons. Raising mineral nitrogen fertilizer level from 45 to 60 and 75 kg N/fed . resulted significant increa5es in boll weight, seed index, seed cotton yield, oü content, oil yield and Hnt yield . Al N,P and K contents of cotton leaves in both seasons. Inoculation of seed cotton with biofertilizer Nitrobien resulted significant increases ¡n bol! weight, seed index1 seed cotton yield, oil contents, lint yield and N,P and K contents of cotton leaves compared with uninoculation treatments ¡n both seasons. The interaction between farmyard manure and nitrogen fertilizer showed that, the highest seed cotton yie?d was obtained with adding 2Om3ìfed farmyard manure and 75 kg N/fed in both seasons. The interaction between mineral nitrogen and bio fertiLization had significant effect on boll weight, seed index, seed cotton yield, seed yield, and oil yield in both seasons. Although the maximum seed cotton rieId and its components were recordedwith using 75 kg N/fed. and adding 20m farmyard manure or using nitrogen biofertikzation. However, using rate of 60 kg N/fed. with application of 20m3/fed. farmyard manure or inoculation with biofertilization were most compatible, since ¡t has the highest seed cotton yield over control. Finally, ¡t could be recommended that, using 20m3 farmyard manure or inoculation seed cotton by nitràgen biofertilization under using 80% of N recommended dose of mineral nitrogen fertilizer (i.e 60 kg N/fed). achieve the maximum cotton yield as well as reducing mineral fertilization and soil pollution under the conditions of the current study.