Photoluminescent polystyrene (PS)/polythiophene (PTh) particles with a core/shell structure were synthesized via a one-step process using radical polymerization for styrene and Fe3+-catalyzed oxidative polymerization for thiophene. Water-soluble potassium persulfate (KPS) and iron chloride (FeCl3) were used as intitiators for the polymerization of styrene and thiophene, respectively. Sodium dodecyl sulfate (SDS) served as a polymierization site in the form of a micelle as well as a collodial stabilizer. Analyzing the samples using field-emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) spectroscopy at different times revealed a plausible mechanism for the formation of the PS/PTh particles. In the mechanism of particle formation, the sulfate (OSO3- ) groups of SDS electrostatically induced Fe3+ ions to the perimeter of the micelle; thus, the polymerization of thiophene was carried out mainly at the perimeter of the SDS micelle, eventually forming small PTh aggregates within the SDS micelles. The styrene oligomers or monomers that shifted into the preformed PTh aggregates were polymerized in the core domain of the aggregates; thus, the particle size gradually increased until all the styrene monomers were consumed, resulting in core/shell PS/PTh particles. The core/shell structure of the PS/PTh particles was confirmed by observing their crumpled morphology after selective dissolution of the PS core using a solvent. The photoluminescence (PL) intensity of the particles was found to be higher than that of pure PTh particles, attributable to the core/shell structure.