In situ observation of lubricant films formed with greases was carried out at EHL (Elastohydrodynamic Lubrication) conditions with a micro-FTIR (Fourier Transform Infrared Spectroscopy). Three urea greases were used and 12 mass percent of the thickener was added in PAO (Poly-α-Olefin). From the in situ IR spectra, the film thickness and the concentration of thickener were estimated from the absorbance of C-H stretching vibration and the ratio of absorbance of N-H and C-H stretching vibration, respectively. Tribo-tests were carried out in sliding/rolling conditions, typically between 0% SRR (Slide/Roll Ratio) and 70% SRR. The traction coefficients were measured with a torque meter attached to the ball shaft. Each thickener was concentrated on ball and disk surfaces. It was found that the concentration of thickener at the Hertzian contact region was dependent on thickener itself under sliding/rolling conditions. It was suggested that an adhesion film by grease thickener had affected on the traction coefficient.