In the present study, the natural enemies of aphids (Hemiptera: Aphididae) and their host plants including herbaceous plants, shrubs and trees were analysed to reveal their biodiversity and disclose tritrophic associations in different habitats of the South Marmara region of northwest Turkey. As a result of field surveys, 58 natural enemy species associated with 43 aphids on 58 different host plants were identified in the region between March of 2017 and November of 2018. In 173 tritrophic natural enemy-aphid-host plant interactions including association records new for Europe and Turkey, there were 21 representatives of the family Coccinellidae (Coleoptera), 14 of the family Syrphidae (Diptera) and 15 of the subfamily Aphidiinae (Hymenoptera), as well as eight other generalist natural enemies. In these interactions, a total of 37 aphid-natural enemy associations-including 19 associations of Acyrthosiphon pisum (Harris) with natural enemies, 16 associations of Therioaphis trifolii (Monell) with natural enemies and two associations of Aphis craccivora Koch with natural enemies-were detected on Medicago sativa L. during the sampling period. Similarly, 12 associations of Myzus cerasi (Fabricius) with natural enemies were revealed on Prunus avium (L.), along with five associations of Brevicoryne brassicae (Linnaeus) with natural enemies (including mostly parasitoid individuals) on Brassica oleracea L. Also in the study, reduviids of the species Zelus renardii (Kolenati) are reported for the first time as new potential aphid biocontrol agents in Turkey. The results of field surveys show that the natural enemies of aphids have high biodiversity, which should be considered in the management of biological pest control.