Precipitation of polystyrene from toluene solution using HFC-134a as antisolvent was investigated. In this gas antisolvent (GAS) precipitation process, the pressurized HFC-134a was dissolved into a 20-g toluene solution containing 5 and 10 wt % polystyrene. The pressure required to expand toluene and cause precipitation of polystyrene by HFC-134a was observed to be much lower than that required by the frequently used antisolvent carbon dioxide. At a temperature of 293 K and a pressure of 5.17 bar, 67 and 74.5% yields were obtained for holding times of 50 and 120 min, respectively. The cloud-point pressure was found to be linearly dependent on temperature. Almost the same yield was obtained for any arbitrary combination of temperature and pressure having the same binary volume expansion. The volume expansion was found to be the major factor influencing yield. The operation with a higher pressure and a lower temperature would result in a higher yield.