Technical Abstract: Mineral content of soybean (Glycine max L. Merr.) seed is one measure of seed quality. The effect of maturity on seed mineral content of soybean seed has not been well investigated in the Early Soybean Production System because maturity is generally confounded with genotypic background effects. Therefore, the effects of maturity on seed mineral concentrations were investigated in two sets of near-isogenic soybean lines derived from either ‘Clark’ or ‘Harosoy’ genotypic backgrounds. For Clark isolines, there were significant (P=0.05) positive correlations between maturity and N and Ca (for N, r=0.83 in 2004 and r=0.62 in 2005; for Ca, r=0.59 in 2004 and r=0.89 in 2005). For Harosoy isolines, there were significant (P=0.05) positive correlations between maturity and Ca and B (for Ca, r=0.60 in 2004 and r=0.83 in 2005; for B, r=0.48 in 2004 and r=0.72 in 2005). Genotypic background effect was highly significant (P<0.001) for N, S, Ca, K, Mg, P, and B seed concentrations. Maturity gene (E-gene) effect was highly (P<0.0001) significant for Ca and B. Commonality analysis showed that the contribution of genotypic background and interactions of genotypic background, maturity, and temperature were greater for N, Ca, Mg, P, B, and Zn. The contribution of either maturity or temperature to total mineral concentration depended on the type of nutrient. Results indicated that, depending on the type of nutrient and year, the contribution of genotypic background or maturity on total variation of nutrient concentrations was greater than that of temperature in most cases. Maturity x genotypic background x temperature interactions also had a significant contribution, reflecting the significance of genotype x environment interactions for mineral nutrients. This information may be useful when developing soybean germplasm with higher mineral seed content.