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Numerous mucoadhesive polymers have been exploited for prolonging the residence time of formulated drugs or pharmaceuticals at specific delivery sites. However, it has been difficult to achieve satisfactory mucoadhesive properties. The two major modification strategies such as thiolation or lectin functionalization have been extensively studied, but disulfide bond reversibility in the case of thiolation and the toxicity of lectins have been problems. Thus, approaches for further improvement of mucoadhesive properties need to be developed. With an overwhelming library of mucoadhesive polymers, one practical way to improve mucoadhesion is chemical modification of existing mucoadhesive polymers. In other words, the method is based on utilizing the cooperative effect that might be achieved by chemical tethering of a small adhesive moiety to an available mucoadhesive polymer. Here, we conjugated catechols derived from mussel adhesive proteins to chitosan, which is a widely known mucoadhesive polymer. We demonstrated that the gastrointestinal (GI) tract retention of chitosan-catechol was improved compared to unmodified chitosan, which is due to the formation of irreversible catechol mediated-crosslinking with mucin. The results indicate that catechol modification of mucoadhesive polymers may possibly lead to a new generation of mucoadhesive polymers for mucosal drug delivery.