Multiprincipal element alloys, which subverts the traditional alloy design concept, have received considerable attention in recent years due to their excellent strength-ductility combination and good corrosion, radiation and wear resistance, etc. These alloys often offers a promising pathway for designing novel metallic materials with unique properties. The active control of the solidification process and its microstructure regulation is an important part of ensuring and optimizing the properties of alloy materials. Currently, undercooled rapid solidification is an effective means to clarify the growth kinetics behavior and microstructure evolution mechanism, as well as to develop the solidification theory. This paper first reviews the dendrite growth kinetics of undercooled multi-principal element alloys. Then, their non-equilibrium solidification microstructures are introduced, together with their mechanical properties. Finally, perspectives on the future research focus, challenges and opportunities of this frontier are provided.