Abstract: An antibacterial surface active agent comprising an effective amount of at least one cyclic amide represented by the general formula ##STR1## wherein R is an alkyl group, alkenyl group, alkylaryl group, alkylarylalkyl group, hydroxyalkyl group, acyl group or hydroxyl-substituted acyl group having 8 to 22 carbon atoms in total, R', R" and R'" are hydrogen atoms or methyl groups, A is hydrogen atom or methyl group, 0.ltoreq.W.ltoreq.1, 0.ltoreq.X+Z.ltoreq.3, 0.ltoreq.Y.ltoreq.3, 0.ltoreq.p+q+r.ltoreq.3, m=1 or 2 and n=2 or 3; said compound may assume a structure in which, if necessary, the nitrogen atoms, except for the amide grouping, may combine with an organic acid radical by covalent bond or to add to an organic or inorganic acid.