The greenhouse whitefly, Trialeurodes vaporariorum is an important pest in vegetable and ornamental crop, especially in greenhouse condition. The predatory mite Amblyseius swirskii has been evaluated as a potential biological control agent for whiteflies. Functional response and mutual interference of adult female of this predator fed on young instars (first + second instar) of greenhouse whitefly were studied in laboratory conditions (25±1 °C, 70±10 % RH, and a photoperiod of 16:8 h L:D). The experiments were carried out on leaf disks in petri dishes with 10-15 replicates. SAS program was used to determine the type of functional responses and estimate the functional responses parameters. Our results revealed that adult females of A. swirskii exhibited type II functional responses on different densities (2, 4, 6, 8, 12, 20, and 30) of prey. The rate of searching efficiency and handling time were estimated as 0.142 ±0.022 h-1 and 2.310±0.110 h, respectively. Nicholson’s model and linear regression were used to determine the per capita searching efficiency and interference coefficient, respectively. The per Capita searching efficiencies of this predator decreased significantly with increasing predator densities and the value of interference coefficient of this predator fed on 40 density of greenhouse whitefly was -0.167. The rate of predation increased as the host density increased from 2 to 30 and subsequently the predator density decreased from 6 to 1. Therefore, different host–predator ratios could affect the efficacy of A. swirskii