The effectiveness of the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), as a suppressive agent of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), was evaluated on greenhouse cucumber at predator:prey release ratios of 1:5, 1:15, and 1:30. Releases at each predator:prey ratio were made at 30 T. urticae densities per leaf. Evaluation was initiated 4 days after the release. On the under side of the leaves which were selected randomly from the lower, middle, and upper parts of the plants, the eggs and active forms of T. urticae and P. persimilis were counted using 10X hand magnifier for each treatment. In control treatments without predatory mite and acaricide application, population of T. urticae was constantly increased and reached 140 active forms/leaf in August. Subsequently the population decreased when the plants died. At ratios of 1:5, P. persimilis reached 8 active forms/leaf while T. urticae populations reached 11 active forms/leaf. At ratios of 1:15 P. persimilis population increased (3.4 active form per leaf) and T. urticae population decreased (1.6 active forms per leaf) in September and the latter one was kept by P. persimilis at low levels thereafter. Plant damage also was significantly reduced at these densities. P. persimilis population decreased when prey (T. urticae) population decreased. Our work demonstrates the potential of P. persimilis to provide effective control of T. urticae on a greenhouse-grown cucumber at a moderately low predator:prey ratio (1:15) in Tokat Province, Turkey.