Abstract: Fungal pathogenicity and fecundity, and effects on population parameters and fecundity of aphids of 4 isolates of Beauveria bassiana were studied (under 21℃, 85% relative humidity). The results show a general consistency between infection mortality to aphids and effect on the reproduction and fecundity of the aphids, but a significant difference among the 4 isolates exists. On the whole, the observed infection rank order of performance of the isolates is “Bb7001”＞“Bb7004”＞“Bb4014”＞“Bb8001”. The aphids' mortality is highest 3～5 days after inoculation of the 4 Beauveria bassiania isolates “Bb7001”，“Bb7004”，“Bb4014” and “Bb8001” with lgLC₅₀ at 3.67，4.34，4.52 and 4.48. The fecundity of aphids is significantly different from the control after inoculated with the isolates in 10⁶ conidia per mL for 3 days. 4 isolates show significant inhibition for reproduction. Within 10 days, the birth rate of aphid offspring decreases by 30.06%～50.00%; the net reproductive rate decreases by 61.90%～72.73%; and the intrinsic increasing rate decreases by 13.04%～41.58%. Among all the isolates, the “Bb7001”exhibits the most significant effect on the green peach aphids and is the first isolate to develop.