Aromatic poly(ether ketone)s were synthesized by the Friedel Crafts polymerization of 2,5-furandicarbonyl dichloride prepared from biomass and petroleum-based aromatic ethers such as diphenyl ether and 1,4-diphenoxybenzene with aluminum chloride (AlCl3). The polymerizations in common molecular solvents such as 1,2-dichloroethane and nitrobenzene did not afford polymers. The Friedel-Crafts polymerization usually undergoes in the swollen gel of the oligomer-AlCl3 complexes; the precipitated physical gels had not been enough swollen. The polymerizations were carried out in various ionic liquids to form swollen gels. The polymerizations proceeded in specific ionic liquid such as 1-butyl-3-methylimidazolium chloride ([C(4)min] CO, and high molecular weight polymers were obtained with good yield. The gels formed in [C(4)mim] Cl were more highly swollen, and additionally the rate constant estimated by the model reaction of 2,5-furandicarbonyl dichloride and anisole was higher in [C4(m)im]Cl than that in 1,2-dichloroethane. The obtained poly(ether ketone)s exhibited good thermal stability and chemical resistance comparable to common poly(ether ketone)s.