This study was carried out at Sids Agric. Res. Sta., Beni-Suef governorate, Egypt, during 2003 and 2004 seasons. The experimental design was randomized complete blocks with four replications, using the Egyptian cotton cultivar Giza 80 (G. barbadense L.,). The treatments were combinations between nitrogen fertilization in two doses (30+30 Kg N/fed.) or three doses (20+20+20 Kg N/fed.) and splitting the dose of mepiquate chloride to two doses (25+25 g a.i./fed.) or three doses (25+12.5+12.5 g a.i./fed.) or (12.5+25+12.5 g a.i./fed.). The spraying timing was at pine head square, at beginning of flowering and after flowering by two weeks. The obtained results revealed that final plant height at harvest, length of internodes, days to appearance of first flower and first boll were decreased significantly in case of treated plants by mepiquate chloride. Also, number of open bolls per plant, yield of seed cotton per plant and per feddan, micronaire reading and specific leaf weight were increased significantly by applying mepiquate chloride. Number of fruiting branches, upper half mean length and seed index were increased by mepiquate chloride in one season. Number of nodes per plant, fresh/dry weight ratio, boll weight, number of plants at harvest, lint percentage, uniformity index, fiber strength, fiber elongation percentage, reflectance and yellowness were insignificantly affected. The highest yield of seed cotton was obtained from the treatments two or three doses of nitrogen fertilization plus mepiquate chloride splitting dose (12.5+25+12.5 g a.i./fed.).