The xylanase inhibitor protein I (XIP-I), recently identified in wheat, inhib-its xylanases belonging to glycoside hydrolase families 10 (GH10) and 11 (GH11). Sequence and structural similarities indicate that XIP-I is related to chitinases of family GH18, despite its lack of enzymatic activity. Here we report the identification and biochemical characterization of a XIP-type inhibitor from rice.