Nanoscale 2,9 dimethyl quinacridone (P.R.122) encapsulated by copolymer of styrene and maleic acid (PSMA) was prepared via phase separation technique followed by the preparation of composite dispersions. Experimental results showed that sodium hydroxide provided the dispersion the smallest particle size and the highest stability when compared with other additives, regardless of it being taken as dispersant or the other neutralization reagent. An optimal process was attained by using sodium hydroxide with a dosage of 0.60 times of molar amount of -COOH groups in PSMA when P.R.122/PSMA composite dispersion was treated at 45 degrees C for 30 min. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 526-531, 2010