Plant density is an essential agronomic practice and affects the productivity of crops. Hence, the optimum plant density to achieve the maximum productivity may vary from crop to crop, genotype to genotype and location to location. Therefore, the current research has been carried out for two consecutive seasons of 2013 and 2014 at the research station of Cukurova University and, the aim of the study was to determine the effect of plant density on seed yield and some agronomical traits in main cropped soybean production. Results of study revealed that seed yield of soybean depends on plant density and highest seed yield (5820.8 kg ha(-1)) was obtained from the 70 cm x 4 cm spacing, while the lowest mean values (3804.5 kg ha(-1)) was obtained from 70 cm x 10 cm spacing. Based on these results, it can be concluded that the maximum seed yield of soybean could be possible with the optimum planting pattern 70 cm x 4 cm or 70 cm x 5 cm for medium early (maturity group 3) varieties in main cropped soybean farming in Adana, Turkey.