High-entropy alloys (HEAs) (or multi-principal component alloys) have been mentioned in different studies because they have good corrosion resistance and mechanical properties, but their biocidal ability is still little explored. The microstructural, magnetic, corrosion, and biocidal behavior of as-cast Al x CoCrCuFe high-entropy alloys with x = 0.5 and 0.9 were analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, magnetization measurements as a function of the applied field, X-ray diffraction patterns, electrochemical essays, and antimicrobial analyses. The results indicated that a higher concentration of Al reduces the saturation magnetization, the corrosion potential, as well as the survival time of the bacterium Escherichia coli on the surface of the studied alloys. The dendritic microstructure was also refined with the increase in the concentration of Al and a higher number of Cu-rich precipitate was observed on their surface. Graphical Abstract