Carboxylated core-shell particles which contain carboxyl groups in the shell polymer swell in aqueous dispersion by electrostatic repulsion between carboxylate ions. Effects of hydrophobic interactions on the swelling of carboxylated coreshell particles were examined by measuring their diameters as a function of various hydrophobicities of the neutralizing amine, the shell polymer, and the dispersion medium. When the dispersion is neutralized by hydrophobic amine which does not contain a hydroxyl group, the swelling is promoted for low pH and suppressed for high pH with increasing the hydrophobicity of the amine. This result suggests that the amine is concentrated near the particle surface by hydrophobic attractions. This concentrated amine promotes dissociation of carboxyl groups of the shell polymer, but combines with dissociated carboxylate ion electrostatically just like a crosslinker. As the hydrophobicity of the amine increases, the amine becomes highly concentrated, and the dissociation of the carboxyl groups and crosslinking are promoted. The swelling is suppressed when the hydrophobicity of shell polymer increases, and that is promoted when the hydrophobicity of dispersion medium increases.