The soybean [Glycine max (L.) Merr.] Iine B739 has the high linolenic acid content in its seed oil. This line was identified from Bay in a mutation breeding program conducted in 1985 at Saga University. The objective of this study was to determine the genetic control of the high linolenic acid content in B739. The line B739 was crossed reciprocally with Bay. There was no maternal and cytoplasmic effects for linolenic acid content in these crosses. For total oil content, no maternal and cytoplasmic effects were also observed. The linolenic acid of F₂ plants of B739 X Bay was segregated in bimodal pattern into normal and high contents which satisfactorily fitted to a 3:1 ratio. This result was consistent with segregation of major gene at a single locus. The allele in B739 was designated lin^h and the genotype for B739 as lin^hlin^h and for Bay as LinLin. The oil content of F₂ plants had an inverse relationship with linolenic acid and when the oil was segregated in bimodal pattern into normal and low contents which satisfactorily fitted to a 3:1 ratio. Thus, it was assumed that the low oil content in B739 was also controlled by this allele. However, Iinolenic acid is the major component in the diet for some mammals, and consequently this allele would be effective to improve the lines with high linolenic acid content.