The quality of injection molded components is significantly dependent on the viscosity of the molten resin. Thus, in predicting and compensating for quality variations, it is essential that the resin viscosity be monitored in an online and automated manner. Accordingly, the present study proposes a method for evaluating the melt quality of the molten resin by means of three pressure sensors installed at the nozzle, runner and mold cavity, respectively. Four melt quality indexes are proposed based on the detected pressure signals, namely the pressure peak index, the viscosity index, the energy index and the pressure gradient. The validity of the proposed indexes is examined under various injection speeds, barrel temperatures and mold temperatures. It is shown that of the four indexes, the pressure peak index is the most strongly associated with the product quality; followed by the energy and viscosity indexes extracted from the nozzle and runner pressure signals. Overall, the results presented in this study show that the proposed monitoring system and quality indexes provide a convenient and effective means of monitoring shot-by-shot variations in the melt quality during continuous injection molding processes. (C) 2018 Elsevier Ltd. All rights reserved.