Abstract: Nowadays, the size of elements in optoelectronic devices has decreased to the micro-nano scale. For more feasible designs and improvement of device performance we need to have a deep understanding of the photophysics of the functional elements and composite systems.In this aspect, ultrafast spectroscopy is a powerful tool for unraveling the excited-state processes in condensed matter. Thus, the combinination of ultrafast spectroscopy with micro-nano photonics not only enables us to understand the fundamental photophysical properties of micro-nano optoelectronic elements and the basic principles of light-matter interactions at the micro-nanoscale, but also helps us to understand the mechanisms of current micro-nano optoelectronic devices. The experimental results from these interdisciplinary studies will also be helpful for the fabrication and improvement of the next generation of devices. Here we first introduce the fundamental principles of ultrafast spectroscopy, then review the recent progress in ultrafast spectroscopic studies on the photophysics of semiconductor nanocrystals and fluorescent carbon anomaterials. Finally, a brief introduction to four-dimensional electron microscopy is presented.