Crosslinkable fluorinated poly(arylene ethers) (FPAE-Fn-PEP) with high transparency and high thermal stability have been investigated for low-loss optical waveguide materials. FPAE-Fn-PEP bearing phenyl ethynyl moiety at the polymer chain end were synthesized by the reaction of 4,4＇-(hexafluoro-isopropylidene)diphenol with an excess decafluorobiphenyl, followed by the reaction of 4-phenyl ethynyl phenol. The M(n)s and M-w/M(n)s of the polymers determined by GPC with polystyrene standard were in the range of 6200 to 19,400 and 1.4 to 2.04, respectively. The resulting polymers were thermally crosslinked at 320 degrees C for 2 h. The cured polymers show good chemical resistance and high thermal stability up to 510 degrees C under nitrogen. The refractive indices of their films were controlled between 1.495 and 1.530 at 1.55 mu m by adjusting molecular weight. A single-mode channel waveguide made of FPAE-F20-PEP was fabricated by conventional photolithography and O-2 reactive ion etching (RIE). The propagation loss of the channel waveguide was measured and found to be less than 0.2 dB/cm at 1.55 mu m.