From the point of view of possible medical applications, biodegradable alloys belong to hot-topic materials. Many different systems are studied in this field, seeking a compromise between mechanical-physical properties vs biocompatibility. Due to a suitable degradation rate, magnesium alloys, including zinc and iron, have been extensively investigated in recent years. The Mg66Zn30Ca4 system is well known for its good mechanical properties and biocompatibility. In this work, we want to present a way how to improve the mechanical properties of this alloy by yttrium substitution. The Mg66−xZn30Ca4Yx (x = 0, 2, 4, 6) ingots were prepared by a rapid solidification process. The mechanical properties of modified alloys were compared with those of the starting alloy. Adding Y (up to 4 at.%) leads to an improvement of ultimate compressive strength. By Tafel plots, the prediction of corrosion rates of analyzed samples was estimated. A higher amount of Y (above 4 at.%) reduces corrosion.