The efficacy of the entomopathogenic fungus Beaveria bassiana Saudi Arabian isolate (B-SA3)was evaluated against the red palm weevil, Rynochophorus ferrungineus (Oliv.).The mentioned isolate was assessed on the different developmental stages of the red palm weevil through toxicity tests, i.e. determination of lethal concentration and lethal times to kill 50% of treated insects. The results showed that 8^th instar larvae were the most tolerant followed by pupa to B.bassiana as their LC₅₀ values were 3.75x 10⁸ and 3.78x 10⁷ conidia/ ml, respectively. Meanwhile, 4^th instar larvae were the most susceptible to infection by B.bassiana (B-SA 3), as LC₅₀ value was 3.25x 10⁶ conidia/ ml, which proved insignificantly different to that determined in adult weevils, i.e. 4.18x 10⁶ conidia /ml. Furthermore, LT₅₀ values were very similar in these latter mentioned developmental stages in any considered concentration; meanwhile, LT₅₀ was much longer in 8^th instar larvae than the other considered instar and/or developmental stages. The fungus B. bassiana was most virulent to eggs of the red palm weevil as none of the eggs hatched following their treatment with any of the considered concentrations (ranging between 5x 10⁹ to 5x10⁵ conidia /ml). Moreover, germination viability of harvested conidia of B.bassiana stored at -4^°C was insignificantly affected up to the 10^th month storage period and was well above 90%. However, germination percentage of conidia then decreased to 70.27% after 16 months of storage. Also, the virulence of the stored conidia was tested after 1, 6, 12 and 16 months on adult red palm weevils, the LC₅₀ values were 3.75x10⁶, 4.66x10⁶, 4.17x10⁷ and 3.37x10⁸ conidia/ ml, respectively. These results show that there was a significant decrease in the virulence of the tested fungus when the duration of storage period was more than 10 months.