A plastic optical fiber (POF) pH sensor is developed based on a sol-gel film. A sol-gel film was prepared by mixing tetramethyl orthosilicate (TMOS), trimethoxymethylsilane (MTMS), ethanol, distilled water and Neutral Red (NR) powder. Then, plastic optical fiber is coated by manually depositing the sol-gel film onto the tip of the POF. The sensing probe is dissolved into analytes with different pH levels, such as Coca-Cola (pH 3), tomato sauce (pH 4), black coffee (pH 5), tea (pH 6), distilled water (pH 7), soap (pH 8), baking soda (pH 9) and Clorox bleach(pH 10). The Refractive index will increase when the analytes are more acidic or more alkaline because they are concentrated with hydrogen and hydroxide ions at pH 3 and pH 10. The output power is varied based on the chemical reaction with the pH sol-gel film in the fiber-optic sensing probe. From the experimental results, it is concluded that the sensitivity of coated POF sensor, which is 0.0566 a.u/RIU, is higher than the sensitivity of the uncoated POF, which is 0.0429 a.u/RIU.