X-ray standing waves generated by periodic multilayers have been used to characterize the interface microstructures of Ti/Ni/Ti trilayers based on the X-ray reflectivity (XRR) and grazing incidence X-ray fluorescence (GIXRF) methods. For the Ni layer having thickness of 1.7 nm, it is observed that the roughness of Ti-on-Ni interface is 0.64 nm and that of Ni-on-Ti interface is 0.40 nm, which can be explained by an additional roughness on the Ti-on-Ni interface induced by the nucleation of Ni crystallites when the Ni layer thickness is at the amorphous-to-crystalline transition region. For the Ni layer thickness of 3.3 nm beyond this transition region, the roughness of Ti-on-Ni interface is 0.42 nm and Ni-on-Ti interface is 0.46 nm, which is consistent with the expectation on wetting and dewetting conditions.