Rice false smut, caused by the fungus Ustilaginoidea virens, is one of the most destructive diseases of rice (Oryza sativa L.) production.As a flower-infecting fungus, how U.virens infects rice in natural conditions remains unclear.We monitored the early processes of fungal infection using in vitro co-cultivation of U.virens strain with young rice panicles on half MS medium.At day 5 after infection, hyphae emerged and enclosed rice spikelets.We observed that hyphae entered florets through the aperture of the apex of glumes, firstly occupied the upper space of the flower organs and formed a threedimensional network, then grew downward to invade the stamens and pistil.We used freshly collected smut balls to observe the processes of U.virens infection and found that U.virens decomposes the contents of the cells, especially, it digests the integuments of ovary.This may be the critical strategy for U.virens to propagate in the infected rice spikelets.We did not observe fungal hyphae in the vascular bundles of pedicel, implicating that U.virens is not a systemic flower-infecting fungus.