Potassium phosphonate is used to control the plant diseases caused by Phytophthora in the word. In the current study, potassium phosphonate is applied on black pepper plant to assess the control effectiveness of quick death caused by Phytophthora capsici. Black pepper vines is treated with phosphonate by root infusion (soaking the roots into the fungicide solution) or soil drenching. After a month, the black pepper leaf specimens were removed for bioassay by inoculation with Phytophthora capsici zoospores suspension in the laboratory condition. Results showed that the lession of leaves from plants treated with phosphonate was smaller area than those collected from plants treated with water. Observed in the field, there was no black pepper plant treated with phosphonate infecting quick death disease while plant untreated with the chemical were infected by the disease. These results provide a scientific basis to recommend farmers using phosphonate for control of black pepper quick death.