PROBLEM TO BE SOLVED: To provide a resin preparation exhibiting long term pest control effect of pest in pest control in water area where water retains such as a water reservoir.SOLUTION: There is provided a resin preparation for controlling pest living in water containing a thermoplastic resin and a pest controlling component of 2 to 3 mass% and having a mesh part, a surface area of the resin preparation per 1 mg of the pest controlling component of 80 to 150 mmand a projection area of the resin preparation per 1 mg of weight of the resin preparation of 0.6 to 1.0 mm.SELECTED DRAWING: None