Provided is a moisturizer having hygroscopicity and water retention ability, and also provided is a composition superior in antiseptic property and feeling on application, in addition to moisturizing property, and free of coloration and odorization.A moisturizer containing acylproline represented by the formula (1) wherein an acyl group represented by R1—CO— is an acyl group derived from a saturated or unsaturated fatty acid having 3-23 carbon atoms, or a salt thereof, and a composition containing (A) acylproline represented by the above formula (1) or a salt thereof and (B) bisphosphonate.