Population dynamics of the naturally occurring phytoseiid Phytoseiulus persimilis Athias-Henriot was studied in relation to Tetranychus cinnabarinus Boisduval in five unsprayed bean plots of 250 m² (10 by 25 m) during 1994 and 1995 in Samandag province of Hatay, Turkey. T. cinnabarinus remained active throughout winter reproducing on a range of ground-cover plants. P. persimilis was generally encountered as gravid females in a non-diapausing phase in debris during winter. Population growth had begun by April on T. cinnabarinus-infested weeds such as Malva neglecta Wallr., Solanum melongena L., and S. nigrum L. In 1994, T. cinnabarinus reached peaks with 15.20±2.40, 11.67±1.70, 22.15±4.06, 25.51±4.43 and 19.0±2.39 total stages/cm² leaf area, from June 28 through July 21 in Fidanli 1, 2, 3, Karacay and Kusalani, respectively (Mean±SE). In the same year, the highest average densities of P. persimilis were 0.89±0.26, 1.59±0.39, 0.81±0.13, 0.43±0.16, and 0.33±0.12/cm² leaf area on July 12 through August 4, respectively. In 1995, peaks of both prey and predator were lower than in 1994 in all plots except T. cinnabarinus in Fidanli 2. The highest average densities of T. cinnabarinus were 11.68±1.69, 14.73±1.65, 13.95±1.98, 0.97±0.25 and 11.59±1.81 total stages/cm² leaf area in Fidanli 1, 2, 3, Karacay and Kusalani, respectively in 1995 with peaks occurring between July 6 and 27. These densities were 0.22±0.06, 0.33±0.06, 0.07±003, 0.01±0.02 and, 0.41±0.09 total stages/cm² leaf for P. persimilis on July 6 through 27 in the above mentioned plots, respectively. Throughout the experiments moderate T. cinnabarinus damage was seen on bean leaves before P. persimilis populations peaked, then the visible damage by pest on host plant diminished due to elimination of the pest by the predator and new leaf formation in both years.