The venting hole of the injection mold is an essential part of mold operation. It makes it possible for the incoming air during filling to be vented out of mold preventing molding defects such as burn mark or short shot. These days resins with many additives such as flame retardant or lubricants are supplied to enhance products quality and processing capability. The resins are likely to produce a large amount of gas during processing. The gas includes organic substances that can easily condense and be accumulated on the surface of the venting hole, which reduces the venting hole to make it difficult for the gas to be vented easily. The mold with clogged venting hole should be cleaned regularly. If the cleaning time could be predicted by monitoring, it can make mold operators to set up the working schedule with proper preparation ahead. In this work, how to measure the temperature and pressure changes of the air in the cavity during filling is examined to make the venting hole clogging to be monitored efficiently. The air in the cavity during filling is compressed adiabatically in a moment due to the fast filling speed. As the venting hole gets clogged, the adiabatic compression would become severe. When the adiabatic compression occurs, the temperature and pressure of the air in the cavity will increase sharply. We developed temperature and pressure sensors to detect the adiabatic compression in the cavity. A sensitivity of the sensors was tested in a compression chamber. A long-term reliability as a sensor was tested by installing them in a mold with various venting hole depths. If we can develop sensors to measure the temperature or pressure changes in the cavity during filling, we are able to monitor the venting hole clogging. We developed and tested methods to measure the temperature and pressure changes in the cavity in this work. We discussed the problems to affect the sensitivity and the long-term reliability of the sensors.