Ips sexdentatus (Boerner) and I. Typographus (Linnaeus)(Coleoptera: Curculionidae) are considered to be important destructive pests of coniferous forests in Europe and Asia. In this study, the efficacy of Beauveria pseudobassiana strain ARSEF 9271 isolated from Dendroctonus micans (Kugelann)(Coleoptera: Curculionidae) was evaluated against I. Sexdentatus and I. Typographus adults. Insects were treated with different conidial concentrations of the fungus to determine the virulence. A conidial suspension of 1× 108 conidia mL-1 caused 100% mortality in both I. Sexdentatus and I. Typographus within 5 and 7 days, respectively. Additionally, 100% mycosis was obtained in the concentration-response experiments for both insects. LC50 values of the fungus were calculated as 3.94× 104 conidia mL-1 and 1.32× 104 conidia mL-1 for I. Sexdentatus and I. Typographus, respectively. I. Sexdentatus and I. Typographus adults were also inoculated with a conidial suspension of 1× 106 conidia mL-1 at inoculation rates of 0%(control), 25%, 50%, 75%, and 100% to determine the horizontal transmission of the fungus. Mortality values from horizontal transmission experiments were determined as 100% at all rates after 15 days at 20 C under laboratory conditions. Our results indicate that B. Pseudobassiana ARSEF 9271 is a promising microbial control agent against the tested Ips species and can horizontally spread among a population of both I. Sexdentatus and I. Typographus.