As a result of breeding experiments using low temperature growth as an index, Mortierella ramanniana mutant MM 15-1, which produces lipids with a high gamma-linolenic acid (GLA) content, was obtained. The results of cultivation experiments in Erlenmeyer Basks showed that although the total lipid produced by the MM15-1 mutant was about 14% lower than that of the parent strain (M. ramanniana IFO 8187), the GLA content of the lipid was 16.5%, which represents about a 2-fold increase over that of the parent strain. In particular, there was a significant increase in the GLA proportion of the phospholipid fraction in the MM15-1 mutant. Furthermore, the results of the lipid composition analysis after phospholipid fractionation by TLC showed that there was a significant increase in the CLA proportions in the phosphatidylethanolamine (PE) and phosphatidylinositol (PI) of the MM 15-1 mutant. When the MM 15-1 mutant was cultivated in a 600-l fermentor, it produced lipid with 18.3% GLA. This was a 2-fold higher than the value obtained with the parent strain under the same cultivation conditions.