Bacillus spp. are known as agricultural biocontrol agents that can produce antifungal compounds. Previous study showed Bacillus siamensis LDR can inhibit several phytopathogenic fungi. In this research, the antagonistic activity of Bacillus siamensis LDR will be evaluated against phytopathogenic fungi, Curvularia lunata BM. The genus Curvularia was reported causing leaf spots and spreading rapidly. This research has isolated black mould from infected coffee leaf (Coffea sp.). The isolation was performed on Potato Dextrose Agar (PDA) and Potato Dextrose Broth (PDB) medium supplemented with chloramphenicol. The result of microscopic and macroscopic observation showed that the characteristics of fungus was referred to genus Curvularia. The molecular identification based on ITS region showed the fungus isolate was belonged to Curvularia lunata with 100% sequence similarity. The antagonist test was carried out using a dual culture method with streak technique. The antagonistic activity of B. siamensis LDR was performed on PDA and compared to modified Czapek-Dox Agar (CDA) using hanjeli (Coix lacryma-jobi) starch as a carbon source. The result showed that B. siamensis LDR was able to inhibit the growth of C. lunata BM on PDA and modified CDA medium. Nevertheless, the percentage inhibition on PDA (63.25%) was higher than on modified CDA medium (42.15%). © 2023 Author(s).