In the real site of engine development, new means are required for optical measurements under a wide variety of conditions including high-loaded operation. We have accordingly developed the new optical probe having less restriction when installing onto the engine as well as having high durability. The shape of connector end of newly developed optical probe that fits to the engine is interchangeable with the M5 sensor used for in-cylinder pressure measurement. The optical module of the optical probe can also be installed in the M10 spark plug or the M8 glow plug. The durability of the newly developed optical probe is; heat up to 400°C, pressure up to 25 MPa, and vibration up to 50 G. The durability of the optical probe was assessed using the engines of commercially available motorcycles. The 110 cm3 engine was used for the time-wise assessment. The 150 cm3 engine was used for the environment-wise assessment. Either one is a single cylinder engine. It has been confirmed that the probe can be used for 40 hours, under severe conditions such as a maximum engine revolution of 11000 rpm. As an example of application of this probe to optical measurements, we conducted spectrometry of combustion light and indicated that it was possible to detect misfire and irregular combustion as well as measuring knocking from the optical emission of 307.5 nm (OH radical).The newly developed optical probe is less restrictive when installing in an engine while having high durability. We anticipate development of various applications using the optical probe to contribute to advancement of internal combustion engines.