Abstract: L-arginine and spermine delayed the degradation of chlorophyll, protein and nucleic acid of excised barley leaves. Comparing with spermine, L-arginine possesed stronger permeability and mobility. Morover, the optimum concentration of L-arginine was 100 folds that of spermine, and the effect of spermine was prior to that of L-arginine. L-arginine incresed the contents of endogenous polyamines of excised leaves, and the abscisic acid which inhibits biosynthesis of polyamines weakened the effects of L-arginine retarding senescence. It was suggested that the conversion of L-arginine to polyamines which are provided with strong physiological activity could be one of mechanisms of L-arginine delaying leaf senescence.