Some cats live at home with their owners while others live unattended on the streets or in shelters. One might expect that the owned cats would be better prepared for diseases with vaccinations, and good care and feeding conditions whereas the stray cats would be prepared for diseases by constant exposure to microbial factors. However, no study has investigated which group has the stronger immune response against diseases. Cytotoxic T cells and NK cells are known to initiate an immune response that causes apoptosis of the affected cells when stimulated by various factors. This immune response occurs due to an influx of perforin and granzyme proteins into the affected cell. Accordingly, this study compared owned and stray cats in terms of perforin and granzymes gene expression. Blood samples were collected from 30 owned and 30 stray cats, whose health conditions were checked. The samples were analyzed by qPCR for perforin, and granzyme A and granzyme B gene expression. All genes were expressed at a higher level in owned cats, although only the granzyme A gene showed a significant difference (p<0.05). This indicates that this gene plays a more active and significant role in cats than perforin and granzyme B, and that owned cats have a stronger immune response to diseases than stray cats.