The predatory bug, Anthocoris minki Dohrn 1860 (Hem.: Anthocoridae), is an important predator of ash psyllid, Psyllopsis repens loginova 1963 (Hem.: psyllidae) and is very abundant on ash trees (Fraxinus excelsior L.) in Mashhad region, Iran. Determining the effects of predation on prey populations is most commonly done through the analysis of functional responses. The functional response of a predator is a key factor regulating the population dynamics of predator-prey systems. The type of functional response and the rates of its parameters (attack rate and handling time) are influenced by different factors. In this study the effect of temperature (15, 24 and 30° C), size of prey (2nd and 4th nymphal instar) ,developmental stage (Adult and nymph), sexuality (female and male) and density of predator (1,2 and 3 individuals) on functional response and its parameters of Anthocoris minki to psyllopsis repense was evaluated in different prey density (5, 10, 15, 30, 60, 100, 150 and 200). Also, the mutual interference of A. minki in three different density (1, 2 and 3 individuals of predator ) was investigated. The experiments were carried out in laboratory conditions: 24 ± 1° c, 70±5 % RH and 16 h: 8 h (L:D) photoperiod. Logistic regression and nonlinear least- square regression were used to estimate the type of functional response and its parameters (a and Th) respectively. To caculate the percapita searching efficiency and interference coefficient, Nicholson’smodel and linear regression were used respectively. The results showed a type II functional response on all treatment except of Adult predator to 2nd stage nymph of prey which exhibited a type III functional response. The greatest value of attack rate was for adult predator in 30°c, and the lowest was for nymph predator to 2nd nymph of prey. The longest handling time was for adult predator in 30°c and the shortest was for density of three predators. The value of interference coefficient was -0.59. The percapita searching efficiency decreased as densities increased but there was no significant difference.