Aims: The aim of this work was to study the biodegradation of benzyldimethylalkylammonium chloride (BAC) by Aeromonas hydrophila sp. K, an organism isolated from polluted soil and capable of utilizing BAC as sole source of carbon and energy. Methods and Results: High performance liquid chromatography and gas chromatography-mass spectrometry (GC-MS) analysis was used to study BAC degradation pathway. It was shown that during BAC biodegradation, formation of benzyldimethylamine, benzylmethylamine, benzylamine, benzaldehyde and benzoic acid occurred. Formation of benzyldimethylamine as the initial metabolite suggested that the cleavage of Calkyl-N bond occurred as the first step of BAC catabolism. Liberation of benzylmethylamine and benzylamine likely resulted from subsequent demethylation reactions, followed by deamination with formation of benzaldehyde. Benzaldehyde was rapidly converted into benzoic acid, which was further degraded. Conclusions: Aer. hydrophila sp. K is able to degrade BAC. A degradation pathway for BAC and related compounds is proposed. Significance and Impact of Study: These findings are significant for understanding biodegradation pathways of benzyl-containing quaternary ammonium compounds.