Oil-insulated transformer is one of the important equipments in the current high-voltage transmission system and it has contributed to the reduction of transmission power loss. However, abnormal phenomena, such as over-heat, discharge and so on, would appear in the oil-insulated transformer. Currently, gas chromatography is the most common diagnosis technique for the transformer diagnosis which is not suitable for rapid detection in the operation field. Therefore, it is necessary to develop a more efficient diagnostic method to identify the abnormal phenomena. In this paper, we demonstrated a platinum modified ZnO gas sensor, which was fabricated by dielectrophoresis (DEP) integration method, to detect acetylene gas dissolved in the insulating oil after arc discharge occurred inside the insulating oil. In addition, the influence of discharge voltage to sensor response was investigated and the response was compared to quantitative analysis obtained by gas chromatography. Relationship between the sensor response and the concentration of acetylene gas dissolved suggested a possibility of quantitative analysis of acetylene by platinum (Pt) decorated ZnO sensor.