Kathon CG, which has a wide area of usage, is one of the representatives of the isothiazolinone group. Considering the application areas in industrial and cosmetic products, it can be a contaminant to water and soil, and it can be toxic to organisms. Vermicompost, known as the organic matter of worms, has important features in terms of increasing the production of plant biomass as well as increasing the soil content. In this study, Kathon CG was applied on the forage pea (Pisum sativum spp. arvence), which is an important food source for humans and animals, and it was treated with liquid vermicompost to reduce the stress caused by the Kathon CG chemical on the plant. As a first step, the EC50/2, EC50, and EC50 x 2 values of Kathon CG were determined. These concentrations were applied to the plant, and the biochemical effects (total protein, H2O2 and MDA amounts, SOD activity) were examined at the end of 48 and 72 h. In the second stage of the experiment, the same chemical was applied with the same amount of liquid vermicompost by keeping the conditions constant, and the same biochemical parameters were examined. The healing properties of vermicompost were compared with and without liquid vermicompost. When statistical data are compared with the control group, the results revealed a significant difference between these two conditions (p < 0.05).