Abstract: The two-spotted spider mite (TSSM), Tetranychus urticae Koch and onion thrips (OT), Thrips tabaci Lindeman, are two serious pests of potato and Orius niger (Wolff) and O. minutus (Linnaeus) are major predators of these pests in the potato fields in Ardabil region. Therefore, we compared the predation potential and fecundity of these predator when they fed on 2nd instar larvae of thrips and female mites on potato leaves in the no-choice and choice experiments in a growth chamber that was set at 24 ± 1 °C, 50 ± 5% RH and 16: 8 h (L:D) photoperiod. In the no-choice tests, O. niger showed lower nymphal mortality percentage, higher fecundity and higher killing rate (km) when fed on 2nd instar larvae of thrips than female mites. O. minutus showed lower nymphal mortality percentage, higher fecundity and higher killing rate (km) on female mites than 2nd instar larvae of thrips. In the choice tests, the number of 2nd instar larvae of thrips consumed by different nymphal instars and the adult pairs of O. niger were significantly higher than the number of female mites consumed. Different nymphal instars and the adult pairs of O. minutus consumed significantly more female mites compare to 2nd instar larvae of thrips. Based on these results it can be concluded that O. niger and O. minutus are effective natural enemies of OT and TSSM in the potato fields, respectively.