Potassium efficiency of soybean genotypes 94065-2 (tolerance of low potassium) and 95137 (sensitive to low potassium) was studied in solution culture with 4 different potassium concentrations. Some root morphological parameters, root activity and yield of 94065-2 were superior to those of 95137 under low K stress. There was significant difference in efficiency of potassium uptaken between the two soybean genotypes, but no remarkable difference in potassium utilization ratio. The high potassium efficiency of 94065-2 might be attributed to its stronger ability to absorb potassium.