Carboxyl group-containing polymer particles giving a neutralized viscous liquid being excellent in gel appearance and transparency. Carboxyl group-containing polymer particles comprising 55 to 94% by volume of water-swelled gel particles having a particle diameter of less than 50 m when the carboxyl group-containing polymer particles are dispersed and swelled in water in a concentration of 0.5% by weight, and 6 to 45% by volume of water-swelled gel particles having a particle diameter of at least 50 m when carboxyl group-containing polymer gel particles are dispersed and swelled in water in a concentration of 0.5% by weight.