【Background】Red imported fire ant (RIFA), Solenopsis invicta Buren, is one of the most devastating pests in the world. Entomopathengenic fungi have been applied to control many crops insect pests successfully worldwide and may be a promising control for RIFA. The effect of temperature on pathogenicity of strain Bb04 of Bearveria bassiana, a suitable candidate to the RIFA workers, was studied in the laboratory. 【Method】The RIFA workers were infected with two concentrations of B.bassiana spore suspension (1×105 conidia·mL-1 and 1×108 conidia·mL-1) and kept under 17, 21, 25, 29 and 33 ℃ conditions. 【Result】The results showed there were significant differences in virulence of Bb04 to RIFA under different temperatures. When workers of RIFA were treated with 1×108 conidia·mL-1, the total mortality of infected RIFA after 15 days reached as high as 100% under 21 ℃, 25 ℃ and 29 ℃. Total mortality was 99.36％ at 17 ℃ and 98.74％ at 33 ℃. However, after 15 days with an infection rate of 1×105 conidia/mL, total mortalities of treated workers at 17 ℃, 21 ℃, 25 ℃, 29 ℃ and 33 ℃ were only 16.83%, 29.42％,36.18％,33.17％and 27.21％, respectively. At 17, 21 and 25 ℃, LT50 values of Bb04 against RIFA decreased from 5.41 at 17 ℃ to 3.88 at 21 ℃ and then 2.57 days at 25 ℃. LT50 increased again to 2.97 at 29 ℃ and 5.11 at 33 ℃. 【Conclusion and significance】25 ℃ was the most effective temperature to promote infection of RIFA by Bb04 and should be applied in both spring and autumn in the field.