Some traditional fermented dairy products like Egyptian Kareish cheese are manufactured in farmhouses following traditional techniques using raw milk without heat treatment or the addition of selected starter cultures, Kareish samples were examined for total aerobic plate count, Enterobacteriaceae, yeast, molds, and staphylococci. The results of the microbiological examination revealed the presence of high numbers of investigated microbes, showing the poor sanitary practice of Kareish cheese production, beginning with the use of poor raw milk quality and processing in unregulated situations. Antimicrobial nanoparticles (NPs) are an innovative method of ensuring the safety of milk and milk products. The present study investigated the effect of selenium NPs (Se-NPs) on the count of undesirable microorganisms. The concentrations of used nanoparticles were 0.5%, 1%, and 1.5% for Se-NPs, they were used to improve the microbial properties of Kareish cheese samples during storage at the refrigerated temperature of 4°C. The study found that Se-NPs had strong antibacterial efficacy against the pathogens tested at all doses. Conclusion: These NPs have the potential to be used as preservatives in milk and milk-based products like Kareish cheese. Additionally, raising the concentration of these NPs by 1.5% Se-NPS increased their effects.