Predation ability is a key component determining the suppression of agricultural pests by natural enemies. The aim of this study is to evaluate the effect of prey density and developmental stage on the predation of Euseius scutalis (Acari: Phytoseiidae) on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) and the oriental red mite, Eutetranychus orientalis (Acari: Tetranychidae). For this purpose, laboratory functional response experiments were conducted using female adults of E. scutalis. Results indicated that the predator causes an inverse density dependent mortality to larvae, nymphs and adults of the two-spotted spider mite, as well as the oriental red mite. The random predator equation was used to fit the data. E. scutalis handling time increased significantly with T. urticae and E. orientalis developmental stage. The maximum number of T. urticae prey consumed was 48.3 larvae, 28.5 nymphs and 11.0 adults, where the corresponding values for E. orientalis were 48.8, 32.2 and 18.2 larvae, nymphs and adults, respectively. Estimated handling times and attack rates of E. scutalis on larvae, nymphs and adults of T. urticae were 0.4970 h and 0.1058 h^-1, 0.8435 h and 0.1395 h^-1, and 2.1834 h and 0.0835 h^-1, respectively. The corresponding values on larvae, nymphs and adults of E. orientalis were 0.4920 h and 0.1166 h^-1, 0.7452 h and 0.1361 h^-1, and 1.3186 h and 0.0597 h^-1, respectively. The results of this study may be indicative of the predation ability of adults of E. scutalis on these notorious pests, providing a basis for determining release rates appropriate for various pest densities.