In this study Staphylococcus aureus strain isolated from bovine mastitic milk was subjected to different heat treatments (25, 37 and 50ºC) for 24 and 48 hrs. Each time the heat treated strain was incubated with bovine lymphocytes in vitro. One dimentional SDS-PAGE and dendrogram analysis were applied on the extracted heat shock proteins (HSPs) that were expressed from Staphylococcus aureus strain when it was incubated at the same temperatures for the same incubation times. Transformation assay using MTT reduction showed highly significant stimulation in response to phytoheamagglutinin when incubated with 50ºC heat treated Staphylococcus aureus for 24 and 48 hrs. The SDS-PAGE revealed that HSPs70 were highly expressed by 22.7% when the Staphylococcus aureus strain was exposed to 50ºC for 48 hrs, while the lowest percentage 5.3% was found when it was exposed to 25ºC for 48 hrs. The dendrogram analysis of the HSPs showed that the highest similarity (84.21%) was found between HSPs expressed after exposure of Staphylococcus aureus strain to50ºC for 24 hrs (Lane1) and those exposed to 50ºC for 48 hrs. (Lane2). We concluded that, heat shock proteins have a stimulatory effect on the most important immune cells (lymphocytes) and the electrophoretic profile showed that the increasing time and degree of heat stress produced more prominent level of these heat stress proteins.