As concerns about the pursuit of well-being culture and interest in safe food has increased and demand for organic agricultural products are increasing. This study was conducted to investigate the occurrence pattern of diseases and pests and to select effective organic materials for control of diseases and pests in organic watermelon. The watermelon was damaged by diseases and pests such as Didymella bryoniae, Podosphaera xanthii, Aphis gossypii, Tetranychus urticae, thrips, Spodoptera exigua, and Spodoptera litura. Among them, powdery mildew and cotton aphid are major disease and pest in organic watermelon. The occurrence of powdery mildew and cotton aphid initiated in the middle of May in Chungju and Eumseong. The control efficacy for eleven organic materials against powdery mildew was evaluated. As the results, the symptoms of plant disease were effectively reduced by more than 85% in the treatments of materials such as sodium bicarbonate 80% and sulfur 80%. The treatment of TFM-6 (insect repellent 2%+paraffin oil 68%) and TFM-7(cinnamomum ext. 10%+derris ext. 20% + citranella oil 30%) showed by more than 80% in control efficiency against cotton aphid. Tstudy was supported by the research project of RDA.(Project No.: PJ0125302018)