The paper examines the microstructure of a new promising rare-earth magnesium alloy Mg-9Gd-4Y-1Zn-0.5Zr (wt.%) following extrusion and directional cutting, as well as subsequent quasi-static and high-speed compression tests, including the Taylor test. This alloy is characterized by a small number of twins, usually inherent in magnesium alloys, since the mechanism of plastic deformation changes due to rare-earth-doped elements. The microstructure was studied by optical and scanning electron microscopy. Zr-rich intermetallic phases are observed, which can lead to the formation of cracks in the vicinity of the precipitates and local embrittlement of the alloy, as well as various phases. It is noted that with an increase in the strain rate, the nature of the fracture becomes increasingly brittle, as well as individual areas of melting at a strain rate of about 6000 s−1. Microhardness data for samples tested at different strain rates were also obtained. Local areas of dynamic recrystallization (DRX) are observed after high-speed testing, and grain growth is also observed with increasing strain rate, which most likely indicates post-dynamic grain growth. Novel findings regarding compression behavior provide new insights into the mechanisms of plastic deformation and fracture of the alloy under study, as well as some features for future applications. © 2025, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.