A novel plant growth-promoting agent and a plant growth-promoting method using the same are provided. The plant growth-promoting agent contains a lactic acid bacterium having a plant growth-promoting action. Also, in the plant growth-promoting method, a seed, a plant body and/or a soil is treated with a lactic acid bacterium having a plant growth-promoting action. Lactobacillus plantarum strain FERM BP-21501 is suitable as the lactic acid bacterium having a plant growth-promoting action.
