Abstract--In recent years portable, sensitive and cheap sensors have gained interest in fields such as medical diagnostics, food quality control, environmental monitoring and drug development. Especially optical sensors in silicon-on-insulator have proven to be very promising, because they have a low limit of detection, are very compact and can be made with cheap mass fabrication techniques. While a lot of progress has been made to implement such sensors in small and easy to use cartridges, many applications require a sensor probe that can perform measurements at locations that are hard to reach. We introduce a method to integrate a silicon-on-insulator photonic sensor on the facet of a standard single-mode optical fiber, and apply this method to a well-known ring resonator refractive index sensor without deteriorating its sensitivity. We thus combined the good performance of silicon-on-insulator sensors with the high mobility of optical fibers.Index Terms-Optical fiber probe sensor, ring resonator, Silicon-On-Insulator (SOI).