An agent for improving lawn grass quality, which is excellent in promoting dwarfing of lawn grass, making the stem sturdy, increasing the leaf count, and improving greenness and is provided. An agent for improving lawn grass quality containing, as active ingredients and 5-aminolevulinic acid represented by formula (1): R 2 R 1 NCH 2 COCH 2 CH 2 COR 3 (1) wherein R 1 and R 2 each independently represent a hydrogen atom, an alkyl group, an acyl group, an alkoxycarbonyl group and an aryl group or an aralkyl group and R 3 represents a hydroxyl group, an alkoxy group, an acyloxy group, an alkoxycarbonyloxy group, an aryloxy group, an aralkyloxy group or an amino group, or a derivative thereof or a salt of the acid or the derivative and a gibberellin biosynthesis inhibiter.
