Bacillus spp. are potential biocontrol agent that commonly used to reduce contamination on crop caused by microorganism, especially fungi. The purpose of this research is to investigate the antagonistic activity of B. siamensis LDR towards fungal crop contaminant (Aspergillus flavus AHM, Aspergillus clavatus ABH, and Aspergillus tamarii KCP). Antagonist assay was conducted using the dual culture method, streak and pour plate technique. The streak technique showed B. siamensis LDR can inhibit the A. flavus AHM, A. clavatus ABH, and A. tamarii KCP with percent inhibition of 42.75 %, 58.89 %, and 28.46 %, respectively. Meanwhile, the pour plate technique represented higher percent inhibition of A. flavus AHM, A. clavatus ABH, and A. tamarii KCP, 89.28 %, 87.32 %, and 66.35 %, respectively. © Published under licence by IOP Publishing Ltd.