Inoue, I. Hara, T. Inubushi, Y. Tanaka, H. Yabashi, M. JACoW Publishing Geneva, Switzerland Optical pulses and particle beams with ultrashort temporal duration have been powerful probes for capturing ultrafast processes. An X-ray free-electron laser (XFEL) based on the self-amplified spontaneous emission scheme is a newly developed ultrafast light source with femtosecond duration. The ultrafast XFEL pulses are generated from the electron bunches (e-bunches) that are accelerated to a relativistic speed with strong compression to a femtosecond regime. Evaluation of the temporal profile of the e-bunch is therefore essential for optimizing accelerator parameters for achieving XFEL amplification, as well as for characterizing the XFEL pulse duration. As a new temporal diagnostic scheme for e-bunches, we recently propose an X-ray intensity interferometry using spontaneous X-ray beam generated by the e-bunch [1]. In this presentation, I will talk about the concept of the X-ray intensity interferometry for determination of ultrashort e-bunch duration. Also, I will report on the temporal diagnostics of 8.1-GeV e-bunch at SPring-8 Angstrom compact free-electron LAser (SACLA) using the X-ray intensity interferometry.