Since X-ray absorption spectroscopy (XAS) is based on transition of an electron from the core-shell to continuum state of the atom, through X-ray resonances, it also allows studies of the electronic structure of the target atom environment within a molecule. A recent developed spectroscopic technique, so-called ultrafast X-ray absorption spectroscopy, allows to study transient states of atom and molecules. When a pumping laser is implemented to initialize a photochemical process and X-ray absorption spectra are measured at different time delays with respect to the pumping laser, one can achieve the evolution of molecular structure and its electronic transitions. This powerful spectroscopic tool has recently been developed and provided new insights into the ultrafast process such as light-induced spin cross-over in iron tris bypiridine or revealed the hydration structure change of iodide. It will be helpful to investigate multielectron charge accumulation process in molecules for artificial photosynthesis applications.