Botryodiplodia theobromae is the predominant fungus causing sapstain in rubberwood in Kerala, India. The fungus causes up to 12.2 percent weight loss in rubberwood over a period of sixteen weeks. Transmission Electron Microscopy (TEM) of sapstained rubberwood provided evidence on hyphal invasion of cells by B. theobrormae through the pit region, facilitated by its ability to degrade pit membranes. The study also revealed that B. theobromae caused degradation of lignified cell walls by erosion of the cell wall surfaces of wood elements.