This study examined the antimold effect of ultrasonic treatment on Moso bamboo. Six different ultrasonic processes were conducted, and mold development was observed after 4-week high-humidity conditioning. The results showed that the mold rate of bamboo decreased after ultrasonic treatment, which was inversely proportional to the power and duration of treatment time. Scanning electron microscopic analysis revealed that the starch granules largely disappeared after ultrasonic treatment, which likely occurred because the ultrasonic wave broke or gelatinized the starch and widened the pits of the cell wall so that the starch could easily flow out resulting in slightly reduced mold growth.