Pink rot caused by Trichotethium roseum is one of the most important postharvest pathogens of muskmelon in China. In this paper, the effect of Si on growth and histolology of T. roseum was studied in vitro. The results indicated that Si significantly inhibited mycelial growth and spores germination, increased cell membrane permeability of hyphal. The inhibiting effect was enhanced with the concentration of Si increasing. Some morphological changes were observed by scanning electron microscopy (SEM) including intertwisting hyphal, distortion and swelling. Ultrastructural alterations of hyphae were also observed using transmission electron microscopy (TEM). The changes involved increasing of vacuoles in the cell, cell organelle dissolved, cell membrane crimple, considerable thickening of the hyphal cell walls and cell wall disruption. It is suggested that Si directly inhibits growth of T. roseum by changing the morphology of mycelium.