In this study, a new medium-entropy super-austenitic stainless steel with mixing entropy of -1.3R was developed. The effects of Cu precipitation on mechanical properties, corrosion resistance and antibacterial performance after solution and aging treatments were investigated by transmission electron microscopy, electrochemical corrosion, and antibacterial test. The results showed that, after solution treatment, the single-phase austenitic steel was obtained and it has good corrosion resistance and excellent combination of strength and ductility due to high strain hardenability by shear-band-induced plasticity. After aging treatment, coherent Cu-rich precipitates with sizes of about 2-5 nm were observed homogeneously distributed in the austenite matrix, leading to a higher strength without much scarification of uniform elongation. Moreover, Cu precipitation greatly enhanced antibacterial ability but slightly declined corrosion resistance of the steel. Based on our current results, high-entropy concepts can be successfully applied to design new multifunctional super-austenitic stainless steel.