To provide a cylinder liner capable of improving fuel consumption by lessening cooling loss in a cylinder bore (in a cylinder liner tube) concerning to the cylinder liner inserted and retained in a cylinder block.

In the cylinder liner 10 retained by inserting into the cylinder block 2, a groove 11 is formed on an outer periphery of the cylinder liner 10. When a groove depth rate of the groove 11 against the cylinder liner 10 in a radial direction is set up to be smaller, a groove area rate of the groove 11 against an outer peripheral area of the cylinder liner 10 is set up to be larger.