Aims: Optimal production conditions of conjugated gamma-linolenic acid (CGLA) from gamma-linolenic acid using washed cells of Lactobacillus plantarum AKU 1009a as catalysts were investigated. Methods and Results: Washed cells of Lact. plantarum AKU 1009a exhibiting a high level of CGLA productivity were obtained by cultivation in a nutrient medium supplemented with 0 center dot 03% (w/v) alpha-linolenic acid as an inducer. Under the optimal reaction conditions with 13 mg ml-1 gamma-linolenic acid as a substrate in 5 -ml reaction volume, the washed cells [32% (wet cells, w/v) corresponding to 46 mg ml-1 dry cells] as the catalysts produced 8 center dot 8 mg CGLA per millilitre reaction mixture (68% molar yield) in 27 h. The produced CGLA was a mixture of two isomers, i.e., cis-6,cis-9,trans-11-octadecatrienoic acid (CGLA1, 40% of total CGLA) and cis-6,trans-9,trans-11-octadecatrienoic acid (CGLA2, 60% of total CGLA), and accounted for 66% of total fatty acid obtained. The CGLA produced was obtained as free fatty acids adsorbed mostly on the surface of the cells of Lact. plantarum AKU1009a. Conclusion: The practical process of CGLA production from gamma-linolenic acid using washed cells of Lact. plantarum AKU 1009a was successfully established. Significance and Impact of the Study: We presented the first example of microbial production of CGLA. CGLA produced by the process is valuable for evaluating their physiological and nutritional effects, and chemical characteristics.