To provide a cylinder liner for insert casting which is excellent in thermal conductivity with a cylinder block.

In the cylinder liner 2 for the insert casting having an outer circumferential surface 4 on which protrusions with the heights of 0.3-1.2 mm including undercut parts 6 are formed at a density of 20-80/cm2 of protrusions 5, and over which a thermally sprayed layer 7 is laid, the thermally sprayed layer 7 is formed of a ferrous material, and the ratio of a surface area of the thermally sprayed layer 7 in a predetermined area of the outer circumferential surface 4 of the liner to a surface area of the predetermined area is 12 to 23. The thickness of the thermally sprayed layer is preferably 0.01-0.2 mm. The thermally sprayed layer is preferably formed of a thermal spray material in the shape of a wire.