Studies of the concentration dependence of electric conductivity and pH for aqueous solutions of the light fullerene – C60[=C(COOH)2]3 tris-malonate were performed at 25 ◦C. From both data (from the equivalent electric conductivity and pH), the apparent degree of dissociation and concentration dissociation constants of C60[=C(COOH)2]3 in aqueous solutions were calculated. Thermodynamic dissociation constants of C60[=C(COOH)2]3 in aqueous solutions, calculated for infinitely dilute solutions by the both methods, were reasonably similar.