Introduction: Axillary malodor is caused by microbial biotransformation of non-smelling molecules present in apocrine secretions, into volatile odorous molecules. This study aimed to determine the antimicrobial activities of potassium aluminium salts (alum) against four malodorproducing axillary bacterial flora, as an alternative natural product for reducing axillary malodor. Methods: The antimicrobial activity of alum against axillary bacterial flora [Micrococcus luteus (ATCC 49732) (M. luteus), Staphylococcus epidermidis (ATCC 14990) (S. epidermidis), Corynebacterium xerosis (ATCC BAA-1293) C. xerosis and Bacilus subtilis (ATCC 19659) (B. subtilis)], was tested in vitro using broth dilution method for different concentrations (0.937 – 20mg/mL) on Luria-Bertani broth. Subculture was done to determine colony-forming units (CFUs) and the minimum inhibitory concentrations (MICs). Results: Alum showed excellent inhibitory effects on all tested bacteria. The lowest MIC of alum was against C. xerosis, at 1.88 mg/mL. M. luteus, B. subtilis and S.epidermidis showed a higher MIC of 3.75, 5.00 and 7.50 mg/mL, respectively. All of the tested bacteria were completely inhibited at a concentration of 7.50 mg/mL. Conclusions: This study revealed that alum has excellent antimicrobial effects against axillary malodor -producing bacteria and is recommended to be used either directly by topical application or as an active ingredient in deodorants and antiperspirants.