Nanoscale azo pigment yellow 13 (PY13) was coated by poly(styrene-maleic acid) (PSMA) with a free-radical precipitation polymerization, followed by the preparation of the dispersion. The effects of the PSMA structure on the particle size and centrifugal stability were investigated. The experimental results revealed that the particle size was large, and the stability of the PY13/PSMA dispersions was high when the molar ratio of the feeding maleic acid to styrene, the weight ratio of the feeding initiator to monomer, and the weight ratio of the feeding monomer to pigment were about 1.0, 0.6, and 20%, respectively. Fourier transform infrared spectroscopy, dynamic light scattering, and transmission electron microscopy indicated that PY13 was coated by PSMA. The PY13/PSMA dispersion was stable in the pH range 5.6-1.0.5. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115:1929-1934, 2010