During routine mass rearing of Culex pipiens L., 46 % mortality rate was recorded among 3-day-old larvae in the late summer, 2014, at Cairo University, Giza, Egypt. An analysis of the water in the rearing plastic cups and the dead larvae revealed the presence of the fungus Nomuraea rileyi (Farlow) Samson. A comparative study was carried out using life-table parameters of the fungal-infected population of Cx. pipiens and fungus-free population (control) under laboratory conditions (30 ± 0.10 °C, RH 52.5 ± 7.8 % and photoperiod 16L:8D). Fungal-infected stages of Cx. pipiens exhibited a decrease in longevity (larvae, 5.89 ± 0.063 days; adult males, 7.8 ± 0.75 days; adult females, 10.83 ± 1.6 days). The mean generation time of the healthy population (22.09 ± 0.82 days) was not significantly different from that of the infected population (22.25 ± 0.08 days), nearly the same mean generation time. The fungal-infected Cx. pipiens population replicated itself 4.62 ± 1.45 times with a very low exponential rate of daily increase of 0.0688 ± 0.0154/day. However, the fungus-free population showed a higher replication rate of 38.10 ± 11.80 times, with a higher daily rate of increase (0.1648 ± 0.0167/day). Females of the fungal-infected Cx. pipiens, exhibited a decrease in the fertility, 25.67 ± 7.70 eggs/female, as compared to the females from the control population, 163.29 ± 40.64 eggs/female. Data of the present study suggested the possibility of using N. rileyi as a safe bio-control agent against the development of the larvae of Cx. pipiens.