Abstract: This study was conducted to identify chemicals in root exudates and their effect on Rhizoctonia solani in potato cropping systems. Root exudates were collected from the fields with 5 years of continuous potato cropping in comparison with rotational cropping of potato and other crops, using inhouse made root boxes at the seedling and squaring stages. Chemicals in the root exudates were identified using the GC-MS method. The results showed that glucide concentration was the highest in the root exudates, followed by organic acids. Compared with the rotational cropping, the continuous cropping significantly decreased the glucide content and increased the content of organic acids in the root exudates. The contents of almitic acid in root exudates under continuous cropping was 0.94% at seedling stage and 1.4% at squaring stage, the dibutyl phthalate was 0.15%, whereas under rotational cropping, those values were decreased to 0.15%, 0.2%, and being negligible, respectively. The root exudates promoted the growth of R. solani, especially under continuous potato cropping. The simulation test showed that the palmitic acid and dibutyl phthalate in root exudates could promote the growth of R. solani.