The catalytic capabilities of acyclic amino acids for the direct asymmetric aldol reactions assisted by 2,4-dinitrophenol in aqueous media were investigated. Several acyclic amino acids catalyzed asymmetric aldol reactions with excellent stereoselectivity, and afforded the corresponding beta-hydroxy ketones in high yields and up to 99% ee. Our result suggested that the L-isoleucine was the most effective one.