A plant-growth promoting agent is provided, which is lower in environmental pollution, highly safe and harmless to human bodies and which exhibits an excellent plant growth promoting action even under wide temperature conditions from low temperatures to high temperatures. And also the plant growth-promoting agent is provided, which has an ability to store ubiquinone, as an active ingredient of the plant-growth promoting agent, in a stable state and can be dispersed and stably present in a medium such as a soil or an aqueous liquid which supplies nutrition to the plant and especially in an initial stage in which a plant body is grown after germination.
