The aim of this research was to determine the genetic variability of chosen soybean lines in seed quality by determining diversity in phenotypic expression of 1000 seed weight, as well as protein and oil concentrations in the seed. Field trials were set up in a randomized, complete block design with two replications, at the Agricultural Institute Osijek during three growing seasons (2010-2012). Each year, after harvest, 1000 seed weight, and protein and oil concentrations in the seed were determined. Statistical analyses of the results included: calculating basic measures of variation and analysis of variance. The analyzed data showed the existence of plant material’s diversity in phenotypic expression of investigated seed quality traits, as well as the existence of statistically significant genotype and year effects.