The effects of potassium ferricyanide, sodium n-dodecyl sulfate, sodium hydroxide and temperature on the molecular weight and the yield of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that oxygen in air had little influence on the oxidative polymerization of 2,6-dimethylphenol (DMP) in the aqueous medium, and potassium ferricyanide was only an oxidant during the oxidative polymerization of DMP. Sodium n-dodecyl sulfate could stabilize polymer particles and facilitate the oxidative polymerization of DMP on the surface of polymer particles, which resulted in the increase of the molecular weight of PPO. The yield and molecular weight of PPO increased significantly with NaOH concentration at first and then decreased with NaOH concentration. The high molecular weight PPO with high yield was obtained at 50°C, but both the yield and molecular weight of PPO decreased with the further increase of temperature.