In these day, polymer thin films is the base of various electronic device. The films need to be stable on solid substrates while processing application to preserve their properties. However, increasing temperature by operation of an electronic device causes polymer thin films lost their stability. In early 21st century, some researcher has discovered that a thermal stability of polymer thin film are enhanced by adding small amount of nano-fillers. This phenomena is different from classical knowledge which the existence of impurity in polymer thin film usually induces dewetting behavior. This research investigates the effects of addition of zinc oxide nanoparticles on thermal stability of polystyrene thin film. The films studied in this work are varied from 10 to 50 nm. The concentrations of zinc oxide nanoparticles are less than 1 wt.%. After annealing the polystyrene thin films for various time, the morphologies are studied by using optical microscope. Dewetting area are observed and calculated to compare the percentages of each samples.