Abstract: The molybdenum blue photometric method was applied to the determination of meta-silicic acid in high sulfur hot spring water. Sulfide (S2-) ion present in the spring water interferred seriouly with the determination of silicic acid and was removed by precipitation with Fe2+ and aging for 1 h. In the filtrate, silicic acid was determined by reaction with ammonium molybdate solution and reduction to molybdenum blue with ascorbic acid. Absorbance of the blue colored solution was measured at the wavelength of 680 nm.