Abstract: In order to study on the feasibility for the enzymatic synthesis of conjugated linoleic acid(CLA), the linoleic acid(LA)isomerase from Propionibacterium acnes was cloned and overexpressed in Escherichia coli, and characterized. The LA isomerase gene(pai)from P. acnes was improved by using codon optimization as E. coli codon usage. The DNA sequence encoding modified LA isomerase was cloned into pET-20b, yielding pET-20b-pai, and transformed into E. coli BL21(DE3). The recombinant LA isomerase had a molecular mass of 48 ku showing mainly in inclusion body on SDS-PAGE. The gene product was purified by Ni-NTA and the activity was 752.3 μmol/(min·mg)after induction and purification. At pH 7.0 and 35 ℃, the activity of enzyme reached the maximum. The purified enzyme was stable from pH 6.5 to pH7.5, and retained approx. 90% of its activity after 2 h at 35 ℃. A low-level inhibition of LA isomerase(22.4%)and(15.8%)was observed with Mn²⁺ and Zn²⁺(1 mmol/L), respectively. The recombinant LA isomerase had a K_m of 1.13 mmol/L and k_cat of 4.67 s^-1 for linoleic acid. The result showed that the P. acnes linoleate isomerase can effectively catalyze LA to trans-10, cis-12 conjugated linoleic acid(t10, c12 CLA).