Abstract: In this study, we observed the interaction between maize root and zoospores of Phytophthora nicotianae, tested the inhibitory activity of maize root exudates against P. nicotianae, and analyzed the antifungal compouds in the maize root exudates using HPLC-MS. The results indicated that maize root could not only attract zoospores into rhizosphere, but also secret some substances to inhibit the swimming of zoospores, even cause the rupture of cystospores. Further studies indicated that maize root exudates showed inhibitory activity against the release of zoospores from sporangia, the germination of cycstospore, and the hyphal growth. The inhibition rate was 73.8%, 87.2% and 55.2% respectively, when the root exudates concentration was 0.90 mg/mL. The DIMBOA, 2,4-dihydroxy- 7-methoxy-2H-1,4-benzoxazin-3(4H)-one, and its degradation substance MBOA (6-methoxy-2-benzoxazolinone) were identified in root exudates by HPLC-MS. MBOA also showed antifungal activity against the hyphal growth of P. nicotianae. The inhibition ratio reached 90.94% when the concentration of MBOA in media was 0.30 mg/mL. In summary, maize root can not only attract the zoospores of P. nicotianae, but also secret antifungal compounds DIMBOA and MBOA. These results are useful for us to rotate maize with tobacco for tobacco black shank control.