Conjugated Linoleic Acid (CLA) was produced from castor oil using washed cells of Lactobacillus plantarum PTCC 1058 and Lactobacillus plantarum subsp. plantarum PTCC1745 as the catalyst. Under the optimal reaction conditions, the washed cells of Lactobacillus plantarum PTCC1058 produced 1661.26 mg of CLA/L reaction mixture (36% yield of production) from 4.6 mg/ml of castor oil after using 15% (w/v) cell for 121 h.The resulting CLA was mixture of two CLA isomers, cis-9, trans-11 (or trans-9, cis- 11)-octadecadienoic acid (CLA1, 44% of total CLA) and trans-10, cis-12-octadecadienoic acid (CLA2, 46% of total CLA). The total production of CLA is extracellular in all of the reactions performed with Lactobacillus plantarum PTCC1058. Also, Lactobacillus plantarum PTCC1745 produced 1590.31 mg of CLA/L reaction mixture (16.5% productionyield) from 9.6 mg/ml of castor oil after using 15% (w/v) cell for 121 h. Therefore, Lactobacillus plantarum PTCC1058 was suggested for CLA production due to its more production ability and CLA extracellular production.