PROBLEM TO BE SOLVED: To provide an electroless plating bath which enables easy and quick formation of a molybdenum trioxide film on a substrate and has high versatility, a method of producing the molybdenum trioxide film and a chemical sensor.SOLUTION: An electroless plating bath is for coating a substrate with a molybdenum trioxide film by immersing the substrate provided with a catalyst and contains at least one of lithium molybdate and sodium molybdate, dimethylamine borane, nitric acid and an alcohol. The electroless plating bath allows easy and quick formation of the molybdenum trioxide film on the substrate and has high versatility, providing excellent productivity of the molybdenum trioxide film by electroless plating.
