Injection molded optical plastic parts require accurate replication of micro-scale features. The effects of melt viscosity and molding conditions on replication of microscopic v-groove features in injection molded parts were examined for PC with different molecular weight. The micro-scale feature size was a continuous v-groove with 20 mu m in depth and 50 mu m in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied in three levels. As the result, the mold temperature had significantly affected replication for all polymers with different molecular weight. Additionally, the molding conditions that lower melt viscosity led to improved replication. In the case of polymer with high molecular weight, the viscosity decreased with increasing melt temperature. It has been found that high replication of micro-scale features could be achieved by higher mold temperature and higher melt temperature even with high viscosity PC.