Abstract: The fly ash cenospheres(FAC)/Mg alloy dissolvable composites with different contents of Al were prepared by stirring cast method. Optical microscopy, SEM and XRD were used to study the microstructure, surface morphology after the dissolution and phases of the dissolution product of the FAC/Mg alloy dissolvable composites. The compression property of the FAC/Mg alloy composite was tested using a mechanical performance testing machine. The electrochemical properties were investigated using electrochemical workstation. The immersion tests of the composites were conducted in potassium chloride (KCl) solution at different temperatures. The results show that the FAC/Mg alloy dissolvable composites are mainly composed of α-Mg matrix, β-Mg₁₇Al₁₂ phase, Mg₂Si phase and MgO phase. The dissolving rate of the FAC/Mg alloy dissolvable composites first enhances and then weakens with the increase of the content of Al. When the content of Al is 15wt%, the FAC/Mg alloy composite has the fastest dissolving rate of 56 mg/(h·cm²) in 3wt% potassium chloride (KCl) at 80℃.The compression strength of FAC/Mg alloy dissolvable composites first increases and then decreases with the increase of Al content, and the compression strengths of the FAC/Mg alloy composites are higher than 300 MPa, the highest strength is 372 MPa.