Provided is a method for inducing immunity of a plant using ultra fine bubble water containing a short-chain aldehyde. The plant immunity induction method according to the present disclosure comprises exposing a plant to ultra fine bubble water containing a short-chain aldehyde and an oily substance. In the ultra fine bubble water, ultra fine bubbles are dispersed in water. The life of the ultra fine bubbles in the ultra fine bubble water tends to be prolonged due to the function of the oily substance. As a result, the short-chain aldehyde is allowed to be stably present around the plant, and therefore plant immunity can be induced easily.