Two field experiments were carried out in Agricultural Experiments and Research Station, Faculty of Agriculture, Cairo University, Giza Egypt during 2005 and 2006 summer seasons to study the effect of two potassium levels (24 and 48 kg K₂O/fad) and three nitrogen fertilizer levels (15, 30 and 45 kg N/fad) on yield and yield associated traits of four soybean varieties (Giza111, Crawford, Giza 35 and Giza 22). Results indicated that plant height in the first season more than that of the second season, while chlorophyll content, number of pods/plant, weight of pods/plant, seed weight/plant, seed index, harvest index and seed yield/fad in the first season  were less than that of  the second season . Increasing potassium fertilization levels leads to an increase in all the studied traits for the tested soybean varieties. While, increasing nitrogen fertilization levels lead to increas in plant height, No. of pods/plant, weight of pods/plant, seed weight/plant, seed index and seed yield/fad. Results obtained revealed that there were highly significant differences among genotypes (Giza111, Crawford, Giza 35 and Giza 22) for all the studied characters. Giza 22 gave the highest seed yield/fad, while Crawford gave the lowest one.