PURPOSE: To obtain a plant-growth promoter containing an organic germanium compound composed of bis-β-ethylcarboxylic acid amide germanium sesquioxide, and capable of promoting the growth of a plant by supplying oxygen directly to the cell of the plant.

CONSTITUTION: The objective plant-growth promoting agent is composed of an organic germanium compound composed of bis-β-ethylcarboxylic acid amide germanium sesquioxide of formula I , or especially bis-β-ethylcarboxylic acid germanium sesquioxide of formula II. The agent breaks the molecular structure of sundry germs by its oxidative activity and kills the germs. When the agent is added to an aqueous solution and absorbed to a plant, oxygen is directly supplied to the plant cell, and the water taken by the plant is decomposed by the sun light using the organic germanium compound as a catalyst to promote the metabolism of the cell remarkably. In addition to the above, the agent has freeze resistance and blossom accelerating action, and is extremely useful.