Four hydroxamic acid derivaties were prepared by reaction of hydroxylamine hydrochloride with dimethylphthalate, dimethylisophthalate, dimethylterephthalate and dimethylsebacate respectively and characterized by IR and elemental analysis. The antibacterial activities to Escherichia coli and Staphylococcus aureus of phthaloyl, isophthaloyl, terephthaloyl and sebacoyl hydroxamic acids have been determined using paper disc method. The result indicates that their antibacterial activities to Escherichia coli are better than that to Staphylococcus aureus and among them the sebacoyl hydroxamic acid is the best one. No linear correlation was observed between the antibacterial activities and the concentration of the compounds, each has its optimum antibacterial concentration.