The percentage variation of resistance of polymer thick film (PTF) resistors has been studied. Two different kinds of polymer resin, i.e., epoxy resin and polyimide resin, as well as four different kinds of carbon black are adopted in the preparations of PTF resistors. Among the four different kinds of carbon black, i.e., ε45, MA-100, MA-600 and HS-500 (all trade names), HS-500 shows the least variation with temperature changes. This can be attributed to the high structure property of HS-500 carbon black. The variation will be lowered down with an increase in the loading fraction of carbon black in PTF resistors. Same tendency will be observed in both epoxy and polyimide resin PTF resistors. However, the variations are smaller in polyimide resin resistors than in epoxy resin resistors. The percentage variations of resistance of PTF resistors, after stored at 120℃ for 1000 hrs, or after 25 cycle thermal shock tests, or dipped in a 200℃ solder pot for three seconds, as well as the variations after the short term overload tests, have also been measured and studied. The variations are still smaller in polyimide resin PTF resistors. A possible explanation on this smaller variation in polyimide resin PTF resistor is also presented.