Cationic polymers (e.g., cationated gelatins, cationated pullulans and poly-L-arginines) have potential to promote transmucosal delivery of peptide and protein drugs without producing any toxic effects on epithelial cells. These cationic polymers could interact with the mucosal membranes and increase the number of pathways for water-soluble macromolecules in the tight junctions. In the case of insulin having negative charges in neutral solutions, interaction between the cationic polymers and insulin is also important to promote suitable delivery. An appropriate interaction can help insulin to access to cell surface, but too strong interaction suppresses insulin absorption. When the absorption-enhancing effects of sperminated pullulans and gelatin having different numbers of amino groups on the pulmonary absorption of insulin in rats were evaluated, their enhancing effects correlated with the amino group content. Cationic polymers having suitable charge density will be useful for pulmonary delivery systems of insulin.