It is known that the addition of an anionic surfactant sodium dodecylsulphate (SDS) drastically increases of an aqueous gelatin. The increase can be caused by both electrostatic and hydrophobic interactions. In the present study, we focused the electrostatic one: the effect of both anionic and cationic surfactants to gelatin were investigated by viscosity measurement and HPLC (GPC). The addition of SDS increases the viscosity of gelatin solution and the GPC pattern obtained with an SDS-containing eluent shifted toward lager molecular weight, suggesting the formation of a large aggregate composed of gelatin and SDS. pH-Dependence of the viscosity suggest that the electrostatic interaction is dominant. On the contrary, the viscosity increase by addition of a cationic surfactant dodecyltrimethylammonium bromide (DTMAB) was much smaller. To comparison between the surfactant types will be discussed