Novel aspartylamide derivatives such as N-(.alpha.-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide, N-.alpha.-7(N'-3,3-dimethylbutylaspartyl)-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide) and the like, and a sweetener containing the above-mentioned derivatives or salts thereof as an active ingredient, is low-calory and which exhibits a high level of stability, an excellent safety and an excellent sweetness.