In this study a series of steam gasification experiments were performed on three thermoplastics - Acrylonitrile butadiene styrene (ABS), Polycarbonate (PC) and Polyethylene (PE), in a batch reactor. The effects of steam flow rate and reactor temperature (600～1000℃.) on the amount of tar, soot and char have been studied. The results were then compared with those of Pyrolysis, from our previous study. In addition time of flight mass spectrometry (TOF-MS) analysis was performed to identify the fingerprints of several different tars. It was found out that steam addition has varying effects on each of the studied polymers. It had a positive effect on soot reduction in the case of ABS and PE; tar reduction in PE; and some char reduction in PC. Temperature increase was found to decrease the relative amount of tar while increasing char production. According to the TOF-MS data, the average molecular weight of tar increases with temperature increase.