NOVELTY - Ion-exchange of a metal acid-salt aqueous solution used as precursor for forming a metal oxide, is carried out to obtain a hydroxide-containing sol. A solution of catalyst metal and organic solvent of alcohol group which are catalyst precursors are added and uniformly disperse-mixed in order to mix catalyst with the sol. The mixed solution is applied on an insulating substrate to a preset film thickness. The formed film is then sintered to form a detection film, and obtain a hydrogen-gas detection sensor.    USE - For manufacturing hydrogen-gas detection sensor (claimed) used in fuel cells, motor vehicles, hydrogen fuel modifiers, containers, and piping for monitoring gas leakage.    ADVANTAGE - The method provides hydrogen-gas detection sensors which enable stable leak detection with high sensitivity. Variation in electroconductivity is reduced.    DETAILED DESCRIPTION - Ion-exchange of a metal acid-salt aqueous solution used as precursor for forming a metal oxide, is carried out to obtain a hydroxide-containing sol. A solution of catalyst metal and organic solvent of alcohol (CnHn+1OH, n is 2 or more) group which are catalyst precursors are added and uniformly disperse-mixed in order to mix catalyst with the sol. The mixed solution is applied on an insulating substrate to a preset film thickness. The formed film is then sintered to form a detection film containing dispersively-supporting catalyst particles on metal-oxide particles, and obtain a hydrogen-gas detection sensor. The sintering temperature is 450-550degreesC. The metal oxide has an average particle diameter of 15-30 nm, and the catalyst has an average particle diameter of 1-20 nm. The metal oxide is molybdenum trioxide, tungstic oxide, titanium dioxide, hydrated iridium, vanadium pentaoxide, and/or nickel oxide. The catalyst is palladium, iridium and/or platinum.    DESCRIPTION OF DRAWING(S) - The figure shows the detection film manufacturing method. (Drawing includes non-English language text)