Fluorinated poly(arylene ether sulfide)s containing an ethynyl group (E-FPAESI) were synthesized by nucleophilic aromatic substitution from 4,4'-(hexafluoroisopropylidene)diphenol (6FBPA) and an excess of pentafluorophenyl sulfide, followed by reaction with 3-ethynylphenol. The molecular weights (M-n's) and polydispersities (M-w/M-n's) of the E-FPAESI determined by GPC with polystyrene standard were in the range 14200-25200 and 2.23-2.47, respectively. The polymer films were fabricated by spin-coating and cross-linked by thermal curing. The cured films had good chemical resistance for common solvents such as acetone, tetrahydrofuran (THF), methylene chloride, chloroform, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The glass transition temperature of E-FPAESI was changed from 120 to 160 degreesC after curing and showed high thermal stability up to 489 degreesC. At 1.55 mum wavelength, the refractive indices and birefringences of the films were in the range 1.5200-1.5515 and 0.0034-0.0044, respectively, depending on feed ratio of 6FBPA and 4,4'-(trifluoromethylphenylisopropylidene)diphenol (3FBPA). The optical loss for E-FPAESI was measured to be less than 0.40 dB/cm.