We examined the viability and morphology of Candida albicans under experimental conditions after treatment with varying concentrations of cinnamaldehyde, the major component of cassia (Cinnamomum cassia), using XTT assay, fluorescent microscopy, scanning electron microscopy, and thin-section electron microscopy. At 10 μg/ml level, cinnamaldehyde inhibited mycelial growth, but did not affect the growth of yeast cells, metabolic activity, cell shape, or the ultrastructure of the cells. At 40 μg/ml level, cinnamaldehyde showed fungicidal activity accompanied by alteration of the membrane and interior of Candida cells. These findings indicate that cinnamaldehyde has both fungistatic and fungicidal activities against C. albicans and affects the structure of the cells.