Monodisperse seeded latex particles with a core-shell morphology were prepared by copolymerizing, via dropwise addition, styrene (St)-methyl methacrylate (MMA)-acrylic acid (AA) or St-MMA-methacrylic acid (MAA) onto monodisperse seed latex particles of P(St-MMA). The seeded particles thus prepared were subjected to an alkali/acid treatment in order to generate pores in the particles. For the same carboxylic acid content, the volume expansion of the particles due to pore generation was higher in the particles containing AA than in those containing MAA. The size of the pores increased with increasing AA content. However, a maximum particle volume expansion of about 50% was observed for the particles containing 8 mol % AA in the monomer mixture employed in the second stage, and an explanation for this optimum is suggested.