The primary goal of this research was to investigate the feasibility of measuring the oil film thickness in a journal bearing using an optical film thickness sensor earlier developed at Michigan Technological University. A bearing oil film thickness testing facility was designed to provide precise control of the sensor calibration and experimental measurements. The calibration of the sensor was achieved by the use of an in-bearing calibration setup that allowed manual changes of film thickness by moving the bearing sensor within the bearing. By varying the speed from 350 to 1100 RPM and the load from 0 to 55 kg in a journal bearing, the sensor was able to measure changes in oil film thickness from 0 to 25 μm. The trends caused by changing the load or speed were seen to be consistent with a mathematical model based on the two dimensional Reynolds equation for journal bearing design. The film thickness measurement technique developed was successful in evaluating the performance of a journal bearing under several operating conditions and should provide an excellent tool to further investigate bearing performance.