An investigation was conducted to determine whether differences in host size of different species affect the body size, fecundity, and longevity of Trissolcus mitsukurii, a solitary egg parasitoid of stink bugs. The eggs of the Pentatomid bugs of Halyomorpha halys (large size), Plautia crossota stali (middle size), and Nezara viridula (small size) were supplied to T. mitsukurii and incubated until progeny emerged at 25±2°C and a photoperiod of LD 16 : 8. Both male and female parasitoids emerged with larger body sizes when they developed in large host eggs such as H. halys. Larger size parasitoids had greater longevity and larger size females showed higher fecundity.