NOVELTY - A hardenable perfluoro polyether gel composition is heat-hardened to produce perfluoro polyether gel hardened material, and acid resistance of hardened material is improved. The gel composition contains (in parts mass) linear perfluoropolyether compound (A) (100) having 2 or more alkenyl groups in one molecule, linear polyfluoro monoalkenyl compound (B) (1-300) having perfluoropolyether structure in principal chain, organosilicon compound (C), hydrosilylation catalyst (D) and non-functional perfluoropolyether compound (E) does not having alkenyl group.    USE - Method for improving acid resistance of perfluoro polyether gel hardened material used for motor vehicles, chemical processing plant, inkjet printer, semiconductor production lines, medical machines, aircrafts, gel products, fuel cells and physical and chemical analysis machines (all claimed).    ADVANTAGE - The perfluoro polyether gel hardened material has excellent heat resistance, oil resistance, chemical resistance, solvent resistance, moisture resistance, and low-temperature characteristics, and low gas permeability.    DETAILED DESCRIPTION - A hardenable perfluoro polyether gel composition is heat-hardened to produce perfluoro polyether gel hardened material, and acid resistance of hardened material is improved. The gel composition contains (in parts mass) linear perfluoropolyether compound (A) (100) having perfluoropolyether structure with -CaF2aO- repeating units in principal chain and 2 or more alkenyl groups in one molecule, linear polyfluoro monoalkenyl compound (B) (1-300) having perfluoropolyether structure in principal chain and one alkenyl group in a molecule, organosilicon compound (C), hydrosilylation reaction catalyst (D) and non-functional perfluoropolyether compound (E) does not having alkenyl group and having perfluoropolyether structure with -CaF2aO- repeating units in principal chain. The compound (A) has weight average molecular weight of 10000-100000. The organosilicon compound is chosen from cyclic organo hydrogen polysiloxane (C-1) having at least one perfluoroalkyl group or monovalent perfluoropolyether group in molecule and/or organosilicon compound (C-2) having perfluoroalkyl group, perfluoroalkylene group, monovalent group and/or bivalent group and comprising H-Si(CH2)xSi- structure. The amount of hydrogen atoms coupled with silicon atom in organosilicon compound is 0.1-5 mol with respect to 1 mol of alkenyl group contained in compounds (A,B).    a=1-6;and    x=1-3.