Abstract: An endophytic actinomycete strain St24 with acaricidal activity was isolated from the root-stem junction of tomato plants, with the taxonomic position of the strain and its control effect against gray mold disease investigated. The St24 was identified as Streptomyces vinaceus, and its broth’s petroleum ether extracts could inhibit a variety of pathogens. The inhibitory effect of the extracts on Botrytis cinerea was the strongest, with the EC₅₀ of inhibiting B. cinerea mycelia growth being 11.78 mg·L^-1. After treated with the extracts, the amount of the mycelia decreased, and the mycelia became crenate or broken, with the protoplast extravasated and the tuberculate malformation appeared. The B. cinerea culture treated with the extracts showed the maximum absorption at 260 nm, which was absent in the control, indicating that the St24 extracts increased the pathogens cell membrane permeability. Pot experiment showed that the extracts could protect tomato plants against B. cinerea. Foliar spraying the extracts at 100 mg·L^-1 had the best protective effect, with the controlling effect reached 94.3% after 24 h and 85.4% after 120 h.