The Pistachio green stink bug, Acrosternum arabicum Wgner is one of the most important pests of pistachio in Iran. Among the egg parasitoids, Trissolcus agriope Kozlov and Lee is an effective biocontrol agent of A. arabicum. For the mass rearing of parasitoids, it is needed to should be host available. Maintenance of host eggs at low temperature (refrigerator) can provide the availability of hosts for parasitoids. One of the important aspects in evaluating the efficiency of a natural enemy is the attack rate across a range of host densities, i.e., it is functional response. In this research, the effect of cold- storage of host egg (1 month at 4 ± 1°C, 65 ± 5% RH, continuous darkness), on the functional response of the parasitoid wasp, T. agriope in difference densities (egg densities of 5,10,15,20,25,30 and 35 egg per parasitoid) was studied in laboratory cundition (27 ± 1°C, 65 ± 5% RH, and 16:8 (L:D)). Logistic regression analysis revealed a type III response on either fresh and cold-stored eggs treatments. Handling times (Th) were similar, with estimated values of 0.76 ± 0.01 and 77 ± 0.01h on fresh and cold-stored eggs, respectively. Also, a similar attack rates were estimated on either treatments. Attack rate (a) was a function of prey density (a= bN), with b averaging 0.017 ± 0.03 and 0.014 ± 0.03 on fresh and cold-stored eggs, respectively. It seems cold storage could be a valuable in mass reared T. agriope and used in biological control programs against A. arabicum.