Bioactive secondary metabolite compounds produced by microorganisms, including bacteria, have certain functions, one of which is to act as antifungal agents. The current study examined the ability of seventeen Bacillus isolates to suppress the soilborne fungus Rhizoctonia solani, determining their potential as biocontrol agents. The KSAR2 isolate was the most effective at inhibiting R. solani mycelial growth, with a 61.2% inhibition rate achieved using the dual culture method. The analysis of the nucleotide sequencing of the 16S rRNA gene indicated that the isolate KSAR2 was identified as Bacillus subtilis and has been deposited in GenBank with the accession number PQ238901. The gas chromatography-mass spectrometry investigation revealed that the most abundant secondary metabolite compounds of KSAR2 were diisooctyl phthalate (38.18%), dibutyl phthalate (9.41%), tris(2,4-di-tert-butylphenyl) phosphate (7.19%), dotriacontane (6.67%), docosane (6.62%), and hexadecanoic acid (4.77%). A study of molecular docking interactions also found that diisooctyl phthalate had the highest binding energy with the fungal chitin synthase, measuring -7.90 kcal/mol. This indicates that interaction with this particular protein could elucidate the mechanism underlying the assessed antifungal activity. Finally, the present study showed that the rhizobacterium B. subtilis strain KSAR2 can inhibit the growth of R. solani. This makes it a promising biocontrol agent for protecting plants against fungal infestations. Furthermore, diisooctyl phthalate may function as a natural, bioactive fungicide by inhibiting chitin synthase in R. solani and potentially other fungi. This could consequently lead to important advancements in the development of novel and potent antifungal agents.