PURPOSE: To obtain a composition capable of continuously releasing an agricultural active substance in a controlled manner.

CONSTITUTION: This composition comprises a water soluble active substance having an agricultural biological action, e.g. a fungicidal agent, a bactericide, an insecticide, a plant growth regulator or a fertilizer, and a water soluble auxiliary for accelerating the release speed and both being dispersed in a silicone rubber matrix (composed of an organic polysiloxane gum, a reinforcing filler and an organic peroxide).