Colletotrichum acutatum is responsible for anthracnose fruit rot, one of the most devastating diseases in strawberry. Phenolic compounds have been described as contributors to anthracnose resistance in strawberry (Fragaria x ananassa, Duch.). Six isolates of Colletotrichum acutatum and four isolates of three other Colletotrichum species, C. gloeosporioides, C. fragariae, and C. graminicola, associated with disease symptoms were investigated in this study. The potential inhibitory effect of phenolic acids (gallic acid, caffeic acid, chlorogenic acid, ferulic acid, trans-cinnamic acid, p-coumaric acid, salicylic acid), flavonoids (catechin, quercetin, naringenin), and ellagic acid, which are naturally found in strawberry, were screened against two different spore suspension concentrations of the Colletotrichum isolates at 5, 10, 50 mM in vitro. Among the phenolic acids and flavonoids tested in this study, only trans-cinnamic acid, ferulic acid, and p-coumaric acid inhibited fungal growth. The inhibitory effects were concentration-dependent but also varied with the spore suspension concentration of the isolates. The results demonstrated that trans-cinnamic acid had the greatest inhibitory effect on all Colletotrichum spp. isolates tested.