Tungsten trioxide is one of the most popular gasochromic materials whose color substantially changes upon exposure to hydrogen gas and is a key material for realizing various optical hydrogen gas sensors. However, it is still required to improve ease of film forming capability and manufacturing, which are also related to gasochromic performance. In the present study, platinum-doped tungsten trioxide (Pt/WO3) films were immobilized onto glass substrates by a sol-gel method, where acetylene-glycol surfactant (Surfynol 465) was investigated as a possible effective additive for the precursor solution. In the hydrogen exposure tests, the films fabricated on a fused-silica substrate and calcined at temperatures less than 350 °C showed weak but clear response characteristics and a high recovery rate because the Surfynol 465 surfactant also functioned as an effective reductant for the Pt precursor solution. The metallic state of Pt in the film calcined at low temperatures was confirmed by X-ray photoelectron spectroscopic analysis. However, the gasochromic performance was completely lost for the film fabricated on a soda-lime glass substrate and calcined at 500 °C. The results suggested that the poisoning effect is attributable to contamination of the film by sodium ions, which can leak from the glass substrate. The film prepared at a low calcination temperature of 350 °C did not suffer severe poisoning and responded to hydrogen gas.