Poly(methacrylic acid-g-ethylene glycol) (P(MAA-g-EG)) has been studied extensively in our laboratory due to its extremely promising applications in the biomedical and pharmaceutical fields. It exhibits pH-responsive interpolymer complexes that make it a promising candidate as an oral carrier for peptide and protein drug. We have developed a photoinitiated free-radical precipitation polymerization method to produce P(MAA-g-EG) nanospheres with relatively narrow size distributions. The influence of various reaction parameters, such as total monomer concentration in water, comonomer molar feed ratios, cross-linking agent concentration, and polymerization time, on the particle size and size distribution was investigated. P(MAA-g-EG) nanospheres with a relatively narrow size distribution could be produced in the size range 150-650 nm depending on the monomer concentration and comonomer molar feed ratio. The P(MAA-g-EG) nanospheres exhibited a pH-responsive swelling behavior. Increasing the concentration of the cross-linking agent during polymerization produced P(MAA-g-EG) nanospheres that swelled to a lesser degree. The morphology of the P(MAA-g-EG) nanospheres was investigated using cryogenic scanning electron microscopy.