An exponential growth has been observed in the last decade where enzymes were used as catalysts for polymerization of different monomers and due to enzyme's origin from natural sources they have been taken as a substitute for the metal-based catalytic systems. Mild polymerization conditions, high enantio- and regio-selectivity and recyclability of enzymes give them an extra edge over the use of organo-metallic catalysts. Though the enzyme-catalyzed polymerizations are environmentally highly advantageous, the high cost, large quantity of enzymes required for polymerization and formation of relatively low molecular weight polymers obstruct their employment in the industry. Due to these reasons, this technique is still at the stage of infancy to generate polymeric materials which can be converted to any useful physical form. In this article enzyme-catalyzed ring-opening polymerization of lactones, lactides, cyclic carbonates and depsipeptides has been reviewed with special focus on the molecular weight of the polymers synthesized hitherto using enzyme catalysis. It is necessary to obtain polymers of sufficient molecular weight from enzyme catalysis to withstand the specific requirements of their end applications if this technique is desired to be escalated to commercial level.