Technical Abstract: A complete understanding of the biosynthetic pathways involved in the formation of soybean seed oils is required to develop lines with useful oil profiles. In particular, modification of the content of saturated fatty acids using genetics has been a target for soybean breeders for many years. One step in the fatty acid biosynthesis pathway in soybean embryos requires keto-acyl-ACP synthase IIa (KASIIa) for the conversion of palmitic acid to stearic acid. Progeny seeds from approximately 5000 NMU-mutagenized lines from the soybean TILLInG population were screened for fatty acid composition. In this screen a number of mutant soybean lines with a heritable increase in seed palmitic acid levels were identified. In a total of five mutagenized lines, candidate gene sequencing revealed potentially damaging single nucleotide changes in the KASIIa gene. In two of these lines, the defect is likely to affect mRNA splicing. Missense mutations (A487T, D406N) were identified in two lines, and one line contained an early termination codon. These mutations represent new mutant alleles of KASIIa available in soybean germplasm. These new alleles may be useful to breeders in order to enhance seed oil content.