Invasive pest species may strongly affect the biotic interactions in agro-ecosystems. Nabis pseudoferus Remane is one of the important predators of Tuta absoluta Meyrick. This pest recently detected in Iran, caused severe damage to tomato production in both protected and open-fields. In this study the prey preference of N. pseudoferus to different stages of two important tomato pests (T.absoluta and Aphis gossypii) was determined under controlled conditions. In the preference test with tomato leaf miner eggs and cotton aphids, beta index of preference for 3rd and 4th N. pseudoferus nymphal instars were obtained as 0.53±0.03 and 0.52±0.03, respectively, which shows a slight preference for the eggs of T. absoluta but, for 5th instar nymphs, males and preovipositing, ovipositing and post ovipositing females, N. pseudoferus tends to feed more on aphids. Furthermore, in choice test between 1st instar larvae of tomato pinworm and cotton aphids, all life stages of N. pseudoferus preferred aphid to first instar larvae of T.absoluta, because 1st instar larvae was hiding inside the leaf tissue. The 3rd instar nymphs of N. pseudoferus preferred cotton aphids to tomato leaf miner 4th instar larvae and Manly's beta index were 0.64±0.04, but the preference index of other life stages of N. pseudoferus to tomato 4th instar tomato leaf miner larvae were as 0.53±0.03, 0.52±0.03, 0.68±0.04, 0.61±0.02, 0.59±0.02 and 0.5±0.05 for 4th instar nymphs, 5th instar nymphs, males, preovipositing, ovipositing and post ovipositing females, respectively.