In this paper, we report for the first time the self-stabilized precipitation polymerization of styrene (St), maleic anhydride (MAH), and acrylamide (AM) in isoamyl acetate as the reaction medium. The effects of various reaction parameters, including the reaction medium, monomer concentration, reaction time, and monomer feed ratio, on the morphology and chemical composition of the resultant poly(St/MAH/AM) terpolymer particles were investigated systematically. The experimental results demonstrated that uniform poly(St/MAH/AM) terpolymer particles with the diameter in the range of 50 to 2000 nm were facilely obtained over a wide range of monomer feed ratios of St/MAH/AM (from 40:40:20 to 10:10:80). Furthermore, the chemical composition of the terpolymer particles was largely dependent on the initial monomer feed ratio, which remained almost constant irrelevant of reaction time when the molar ratio of [St]/[MAH] was 1:1. Therefore, the poly(St/MAH/AM) terpolymer particles with a well-defined morphology, uniform size, and controlled chemical composition can be efficiently synthesized via this method, and the anhydride and amide functional groups provide poly(St/MAH/AM) particles with intensive potential for various applications.