This work investigates an efficient method for purification of simvastatin ammonium salt from the residual amounts of lovastatin ammonium salt. Lovastatin esterase produced by the fungus Clonostachys compactiuscula was chosen as a biocatalyst for selective hydrolysis of lovastatin ammonium salt. Based on specific activities, determined by a spectrophotometric assay, two enzyme preparations were chosen as suitable candidates for this transformation: lovastatin esterase immobilized on Sepharose 4 B or immobilized on diethylaminoethylcellulose. Immobilized enzyme was packed into the inner space of the steel column and examined as a bioreactor in a continuous flow process. Both reactors indicated excellent selectivity ( > 100) and stability.