The rate-accelerating effects of camphorsulfonic acid (CSA) on nitroxide-mediated styrene miniemulsion polymerization were studied. Polymerizations were initiated with benzoyl peroxide (BPO) as an initiator and mediated with either 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) or 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (OH-TEMPO). Although CSA has been used to accelerate the rate in bulk nitroxide-mediated polymerizations, it has not been well studied in emulsion/miniemulsion. With dispersed systems, the effectiveness of CSA is likely to be affected by partitioning between the aqueous and organic phases. In styrene miniemulsion experiments performed over a range of conditions, the effect of adding CSA varied from negligible to significantly increasing the final conversion and molecular weight, depending on the nitroxide:BPO ratio. At a ratio of nitroxide:BPO = 1.7, the effect of CSA addition is small, whereas the final conversion and molecular weight are dramatically enhanced by CSA addition when the nitroxide:BPO ratio is 3:6. CSA is most effective in enhancing the rate and molecular weight when the initial free-nitroxide concentration is higher. The magnitude of the rate and molecular weight enhancement was similar for TEMPO and OH-TEMPO despite their differences in water solubility.