Complex strategies are employed to control pests of stored agricultural products. Tribolium castaneum (the red flour beetle) is is a common pest found worldwide in stored grains. The pest has developed resistance to chemical pesticides, and biological alternatives are the only tool used as a direct control measure. Entomopathogenic nematodes are used in different agricultural systems as biological control agents whose efficiency in plant protection is often comparable to chemical pesticides. An increasing need for the development of new and enhancement of existing biological control agents led us to study the effect of the insecticidal efficacy of two species of entomopathogenic nematodes (Croatian strains: Steinernema feltiae and Heterorhabditis bacteriophora) against T. castaneum larvae and adults. The experiment was set up under laboratory conditions with or without wheat grain as a food attractant for insects. The pathogenicity of IJs of entomopathogenic nematodes was tested in different nematode concentrations, in dark, and under different temperature regimes. The red flour beetle mortality was achieved up to 100% with both nematode species depending on the temperature and nematode concentration. H. bacteriophora and S. feltiae were pathogenic to the red flour beetle even at temperatures lower than 15 °C which is optimal for storing grains. Food attractant did not enhance nematodes pathogenicity. The red flour beetle was susceptible to tested entomopathogenic nematodes and offspring are recovered from the insect cadavers.