The cotton mealybug Phenacoccus solenopsis Tinsley is an important and polyphagous pest, with worldly distribution. This pest causes serious damage to a wide host range such as cotton, sugar cane, China rose shrubs and other important crops and gardens. This pest causes a lot of damage to the ornamental plant of Hibiscus rosa-sinensis L. with the result of drying shrubs at the South and Southwest of Iran. The hymenopterous parasitoid, Aenasius bambawalei Hayat (Hym.: Encyrtide) is one of the natural enemies that has a high potential to control the cotton mealybug in this area. This research was conducted to study the reproductive activity (percent parasitism, percent emergence, and sex ratio) and the immature developmental time of the parasitoid wasp reared on all instar stages (first to third nymphal stages) and female adult cotton mealybug, under laboratory condition, at temperature 25 ± 1°C, 60±5% RH, and a 16:8 (L:D). For this purpose, firstly the synchronous cohort of all growth stages of cotton mealybug was produced. Then the mated females (2 days old) were released singly into a petri dish containing a China rose leaf infested by 30 insect from each growth stage (n = 12, for each treatment). The parasitoid wasps were removed after 24 hours. GLM (Generalized linear models) and SPSS software (ver. 17) were used to analyze data. According to the results, female wasps did not parasitize the first and second nymphal stages. There was a significant difference in sex ratio of A. bambawalei reared on third (23.76 ± 5.77 percent) and adult female (79.73±4.06 percent) stages of cotton mealybug (G1,16 = 54.692, P < 0.001), so the A. bambawalei females preferred to lay their male and female eggs in third nymphal and adult female cotton mealybug, respectively. The percent parasitism (32.50 ± 4.18 vs. 46.66 ± 5.96) and percent emergence (86.46±4.63 vs. 96.33±2.46) of parasitoid wasps was not shown significant difference on the last two mentioned stages, respectively. The immature developmental time of male and female parasitoids was also obtained on the third nymphal stage (17.03 ± 0.14 vs. 17.32 ± 0.48 days, respectively) and female adult (21.30 ± 0.42 vs. 21.67±0.32 days, respectively). The results indicate the high control ability of A. bambawalei, on cotton mealybug.