Abstract: Encarsia bimaculata and Eretmocerus sp. nr. furuhashii are two dominant species of parasitoid parasitizing Bemisia tabaci in South China. Oviposition preference of the two species was studied in the laboratory. The results indicated that both the two species of wasps could parasitize all nymphal stages of B. tabaci. When given a single instar nymphs of B. tabaci, E. bimaculata lay more eggs on the 3rd and 4th instar nymphs than on the 1st and 2nd instars, while Er. sp. nr. furuhashii lay more eggs on the 3rd and 2nd instars than on the 1st and 4th instars. When given all four B. tabaci instars simultaneously, E. bimaculata decreased the parasitization on the 1st and 2nd instar nymphs but increased the parasitization on the 3rd and 4th instar immatures; whereas Er. sp. nr. furuhashii increased its parasitization on the 2nd and 3rd instars but reduced oviposition on the 1st and 4th instars. Host plants showed no influence on the oviposition trends of the two wasps. The results suggested that the 3rd and 4th instar nymphs of B. tabaci were the most suitable hosts for E. bimaculata while the 2nd and 3rd instars were the more suitable for Er. sp. nr. furuhashii.