Aims Aspergillus aculeatus, a pathogen of peaches, can cause soft rot and lead to economic losses in agricultural production. However, studies on the prevention of soft rot caused by A. aculeatus have rarely been reported. Tricyclazole (TCZ) is a fungicide that has been widely used in disease prevention of various crops but the inhibitory mechanism of TCZ on A. aculeatus is unknown. Our aim was to determine the effects of TCZ on A. aculeatus. Methods and Results In our study, TCZ inhibited the growth of fungal colonies when applied at 0 center dot 5-6 mmol l(-1) and inhibited the production of melanin at 3 mmol l(-1). Conidia exposed to TCZ were less effective at causing the disease in inoculated samples, and electrical conductivity, divulgation of nucleic acids and proteins rose with increasing concentrations of TCZ. Microscopic results suggest that TCZ damages not only the cell wall but also the cell membrane. Results of qRT-PCR showed that TCZ had no significant effect on the regulation of genes coding for laccase, apoptosis and hypothetical protein; however, it significantly down-regulated genes coding for cellulase, chitinase and sterol. Conclusions Tricyclazole can influence the pathogenic ability of A. aculeatus by damaging the cell structure of hyphae and conidia, reducing the melanin production, and altering the expression of pathogenic-related gene. Significance and Impact of the Study The results explained the potential cause and mechanism TCZ produced in A. aculeatus. Our research offers scientific insights into future research interest relative to using TCZ in the treatment of soft rot caused by A. aculeatus.