The present invention provides a composition comprising a polymer of a β-hydroxy short-medium chain fatty acid, which is used for delivering the β-hydroxy short-medium chain fatty acid or an oligomer thereof to the large intestine. In case the composition is administrated orally, the composition will be delivered to the large intestine, without being degraded in the stomach or short intestine, and degraded by the large intestinal bacterial flora and release the short-medium chain fatty acid or an oligomer thereof. The released short-medium chain fatty acid or an oligomer thereof has useful physiological activities and is effective for treating or preventing inflammatory diseases or cancer in the large intestine.
