Abstract: Trogoderma granarium Everts is one of the most important economic quarantine peston different kind of stored seeds and products. The control of this insect is very difficult becauseof its biology and ethology. Bioassays with six isolates of the entomopathogenic fungusBeauveria bassiana (Bals.-Criv.) Vuill. were conducted to active larvae (L2-4) and adults ofT. granarium. The treatment was indirectly with conidial suspensions (2×108 conidia/ml) of theisolates. The lethal effect was evaluated as percentages of cumulative daily mortality due tomycoses. The virulence of each fungal isolate was estimated by the values of the median lethaltime (LT50), calculated by probit analysis. Τhe highest lethal effect (100%) to adult insects ofT. granarium in the variant with isolate 501Bb of B. bassiana was recorded on the 13th day and inthe variants with isolates 559Bb and 433Bb on the 15th and 16th day, respectively. Isolates 559Bband 433Bb were with the highest virulence with values of LT50 varying within confidenceintervals from 4.845 to 5.391 days and from 4.914 to 5.719 days, respectively. No significantdifference was recorded between variants at p < 0.05. Results of conducted experiments withactive larvae (L2-4) of T. granarium showed that lethal effect didn‘t reach 100% in all variantseven on the 22nd day. Variants with the highest mortality were with isolates 513Bb (79.59% ±5.84) and 433Bb (69.39% ± 5.14). Isolate 513Bb was with the highest virulence to the larvae ofthe pest with LT50 values within confidence interval from 11.00 to 12.24 days, followed byisolate 501Bb – from 12.44 to 13.96 days. The difference between both isolates was significant atp < 0.05. The presented results of the experiments are the first announcement about bioassay ofentomopathogenic fungi to larvae and adult insects of T. granarium.