Effects of gamma irradiation on chemical, microbiological, and immunological changes of Queso Blanco cheese were investigated. Although Queso Blanco cheese was made by heat pasteurization at 85$^{circ}$C and addition of acid without lactic starter culture, total bacterial counts and lactic acid bacterial counts of control cheese were 7.65${pm}$0.04 and 7.64${pm}$0.02 log CFU/mL, respectively. It was thought that this microbial growth was due to the incomplete inactivation of raw milk by the heat treatment, resulting into growth during the pressing and the drying process. It demonstrated the possibility that if heat- and acid-resistant hazard microbes are present in raw milk, they can grow during the processes. Lactic acid bacterial counts of the irradiated cheese were 5.45${pm}$0.02 log CFU/mL at 1kGy, 2.12${pm}$0.12 log CFU/mL at 2kGy, and not detected at 3kGy or higher doses. The reduction of antigenicity by gamma irradiation was not found. It might be caused by the fact that most whey proteins of milk, a major antigen in milk, were already denaturated by heat process and removed during the draining.