Abstract: The exotic parasitoid Leptomastix dactylopii How. is used in biological control of citrus mealybug, Planococcus citri, one of the main insect pests which causes quality and quantity loss in citrus plantations. The number of parasitized P. citri individuals, parasitization ratio and sex ratio of emerged L. dactylopii adults according to varying host densities were determined at 25 ± 2 °C, 70 ± 10% R.H. and 16 h/day photoperiod conditions. Mated one-day old L. dactylopii females were confined with a sprouted potato infested by P. citri nymphs (N3) and virgin females, with densities of 10, 20, 40, 80 and 100 individuals, and allowed to forage for 72 hours within plastic jars of 10 cm diameter and 9 cm height. Afterwards, L. dactylopii females were removed from jars and P. citri nymphs (N3) and virgin females were checked for mummified individuals, the measure of a successful attack. Parasitoid adults were recorded for 30 days, beginning with the first emergences, which started on the 17th day. As a result of this study, higher attack numbers occurred as the number of mealybugs increased. The parasitization ratio of L. dactylopii was 100% at the lowest host density. The ratio decreased gradually as the host density increased (97.0, 92.0, 84.50 and 70.0%, respectively). The sex ratio was in favour of the parasitoid females for each of the host densities. The type of the parasitoid response to the increasing host densities best fitted to Holling’s type II model, which is considered to be an efficient parasitoid species in biological control of agricultural pests.