The Zhu (Chinese: 柷; pinyin: zhù) was a percussion instrument used in the Confucian court ritual music of ancient China. It consisted of a wooden box (which was often painted red or otherwise decorated) that tapered from the top to the bottom, and was played by grasping a vertical wooden stick and striking it on the bottom face. The instrument was used to mark the beginning of music in the ancient ritual music of China, called yayue. The instrument is rarely used today, with specimens appearing mainly in Chinese museums, although in Taiwan it is still used in Confucian ritual music by the Taiwan Confucian Temple.
The Zhu is mentioned, along with another percussion instrument called Yu (敔), in pre-Qin Dynasty annals, and appears in the Classic of History.
The Korean Chuk (hangul: 축; hanja: 柷), a musical instrument that is essentially identical to the Zhu, from which it was derived, continues to be used in Korean Confucian court ritual music.