Cross-linked polystyrene particles have applications in many fields such as ion exchange columns, fuel cell membranes, and catalysis, to name a few. Synthesis of these particles in smaller sizes offers various advantages due to the increased specific surface area. Polystyrene nanoparticles having volume-equivalent diameters in the range of 40-60 nm were synthesized using emulsion polymerization. Emulsifier-free synthesis was also employed, yielding particles in the size range of 80-90 nm. Sodium styrene sulfonate (NaSS) was used an emulsifying comonomer, and divinyl benzene (DVB) was used as a cross-linking agent. The average particle diameter increased with increasing DVB concentration in the feed. By increasing the NaSS content in the feed from 4 to 28 wt %, the ion exchange capacity of the cross-linked polystyrene particles increased from 0.05 to 2.2 meq/g. The presence Of SO3Na groups in the cross-linked polystyrene particles was also confirmed by using FT-IR, and the intensity of the peaks at 1040 and 1182 cm(-1) increased with increasing NaSS concentration in the feed.