In this study five compositions of CoNiAl alloy with fixed Al content were prepaid to investigate the effect of chemical composition on the microstructure and phase volume fractions. It was found that by increasing Co the volume fraction of β phase increases and by increasing the β phase the grain size will be increased. This increase will be reflected on increasing the hardness of this alloy. Further investigations for the corrosion resistance in simulated body environment were done. It was found that phase volume fractions increased corrosion rate by increasing the volume fraction of β phase.