Recently, it has been reported that fullerene (C60) thin films deposited on Ag(111) surfaces by molecular beam deposition (MBD) have a high degree of crystallinity and are oriented to the substrate surface. However, because there exists only a few characterization methods to directly examine the in-plane structure of the ultrathin film, such as STM, the details were not understood sufficiently. We employed a new system of an energy-dispersive type total-reflection X-ray diffraction (TRXD) method combined with organic molecular beam deposition (OMBD). The TRXD method is developed for the high-sensitivity measurement of the in-plane structure in organic thin films. By using this in situ and real-time observation, the growth process of C60 ultrathin films on Ag(111) surface was observed at the range of a few nanometers. As a result, we confirmed the in-plane structure and the epitaxy on the substrate surface.