The synthesis of poly (phenylene ether) (PPE) has been carried out in supercritical carbon dioxide (scCO2) at 40 oC and 15 MPa with a one-step polymerization. Maximum yield and weight-average molecular weight (Mw) of the synthesized PPO were ca. 70 % and 1.1 104, respectively. The time evolution of the GPC-charts of sample polymer in the reaction suggested that the polymer precipitation occurred in the latter stage of polymerization. This may be one reason for achieving higher molecular weight in this method. Based on the above observation, we made an attempt to carry out two-step polymerization after possible phase separation occurrence. Two-step polymerizations at 55 oC, 22 MPa or 70 oC, 30 MPa for 8 h after synthesis at 40 oC, 15 MPa for 20 h, gave yields and Mw of up to ca. 80 % and 1.9 104, respectively. A small amount of a byproduct, diphenoquinone (DPQ), was found in both one-step (1.4 %) and two-step (ca.1.7 %) polymerizations. The synthesized PPE was found to have similar glass transition temperature (Tg, 200 oC) to that of commercial PPE. In the synthesis, scCO2 seemed to function not only as a reaction solvent but also as a plasticizer for the PPE polymer.