A method of preventing defective germination or rosette formation of a plant seed that tends to suffer from defective germination or rosette formation during growth thereof is provided, which can be easily carried out without using large-scale equipment and makes the sowing after the treatment of the method easy. The method of preventing defective germination or rosette formation of a plant seed includes the steps of: leaving the plant seed to stand in highly watery condition at low temperature in a dark place; and drying the plant seed.