Abstract: To study the effects of tobacco root exudates on Phytophthora nicotianae var. nicotianae, liquid chromatograph-mass spectrometry (LC-MS) was used to measure the contents of common root exudates between Xiaohuangjin 1025 and Gexin 3. Viewing from mycelial growth, sporangia production and mycelial yield, the inhibitory effects of 5 common root exudates whose contents differed significantly between the two varieties were analyzed. A pot experiment was conducted to detect the control effects of 5 common root exudates against tobacco black shank. The results showed that in common root exudates, the contents of tartaric acid, dinitolmide, prohydrojasmon, palmitic acid and oleic acid differed significantly. At a low concentration (100 μg/mL), the inhibition effects of the 5 compounds against P. nicotianae were noticeable. With the increase of concentration, the inhibition effects were raised. The inhibition rates of tartaric acid against mycelial growth and sporangia production were 36.72% and 50.16%, respectively. The inhibition rate of palmitic acid against mycelial yield was 59.86%. The control effect on tartaric acid and palmitic acid against tobacco black shank were 53.11% and 52.70%, respectively. Therefore, tobacco root exudates contain the compounds which can inhibit P. nicotianae and to a certain extent control tobacco black shank disease.