The van der Waals layered material MnBi 2 Te 4 , as a magnetic topological insulator, has attracted tremendous interest for novel physics research in the fields of condensed matter physics and materials science. However, the nonlinear optical properties of MnBi 2 Te 4 and its applications in ultrafast optics have rarely been explored. In this study, high-quality MnBi 2 Te 4 nanosheets have been successfully synthesized by the self-flux method. The morphology, chemical composition, magnetic properties, and nonlinear optical characteristics were systematically investigated. The magnetic transition of MnBi 2 Te 4 was confirmed by a low-temperature spatially resolved spectroscopic technique. The saturable absorption property of MnBi 2 Te 4 was measured by a balanced twin-detector system with a modulation depth of 4.5% and a saturation optical intensity of 2.35 GW/cm 2 . Furthermore, by inserting the MnBi 2 Te 4 -based saturable absorber, a soliton mode-locking laser operating at 1558.8 nm was obtained with a pulse duration of 331 fs. This research will pave the way for applications of the magnetic TI MnBi 2 Te 4 in nonlinear optics and photonics.