Surface characteristics of styrene/acrylamide/acrylic acid copolymer and styrene/2-hydroxyethyl methacrylate/acrylic acid copolymer latexes prepared without emulsifier using potassium persulfate as initiator and their colloidal stabilities were investigated. The negative ζ-potentials decreased with increasing the amount of acrylamide and 2-hydroxyethyl methacrylate copolymerized. In spite of the increase in surface charge density, the negative ζ-potentials decreased through the maximum with increasing pH. The colloidal stabilities for NaCl concentration were remarkably enhanced with increasing both pH and the amount of acrylamide and 2-hydroxyethylmethacrylate. These results suggest that the contration and expansion of water-soluble polymer layer surrounding the particles play an important role in the surface properties.