NOVELTY - A fuel cell (1) comprises anode (2), cathode (3) and a polymer electrolyte membrane (4) comprising polyolefin(s) grafted with side chains containing proton conductive functional groups. The fuel cell has cell resistance value of not higher than 0.3 OMEGA cm2 at 90degreesC, and cell resistance at 20degreesC differing from cell resistance at 90degreesC of an amount not higher than 90% with respect to the value of cell resistance at 90degreesC.    USE - For apparatus, such as electric vehicle transportation and electronic portable device (claimed).    ADVANTAGE - The fuel cells are highly efficient electrochemical energy conversion devices, and uses polymer electrolyte membrane as good proton transfer membrane with low permeability for reactant gases to avoid cross-over phenomena which reduces the performance of fuel cell. The membrane is particularly useful in low temperature direct methanol fuel cell, to enhance the efficiency and electrical performance of the fuel cell by decreasing the methanol cross-over phenomena. The membrane used in the fuel cell has high tensile strength and flexibility.    DETAILED DESCRIPTION - A fuel cell comprises an anode, a cathode and a polymer electrolyte membrane placed between the anode and the cathode. The polymer electrolyte membrane comprises at least one polyolefin grafted with side chains containing proton conductive functional groups. The fuel cell has cell resistance value of not higher than 0.3 OMEGA cm2 at 90degreesC, and cell resistance at 20degreesC differing from cell resistance at 90degreesC of an amount not higher than 90% with respect to the value of cell resistance at 90degreesC.    INDEPENDENT CLAIMS are included for the following:    (1) a polymer electrolyte membrane comprising at least one polyolefin grafted with side chains containing proton conductive functional groups, through an oxygen bridge;    (2) the production of polymer electrolyte membrane; and    (3) an apparatus powered by a fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic representation of a liquid feed organic fuel cell.    fuel cell (1)    anode (2)    cathode (3)    polymer electrolyte membrane (4)    anode compartment (6)    cathode compartment (11)