To provide a cylinder block and a manufacturing method of its cylinder block, capable of providing high strength for a cylinder block upper end part to an open deck type cylinder block.

An MMC sleeve 4 composed of a metallic group composite material is arranged in a close contact state on the outer peripheral side of a cylinder liner 3 in a deck surface 1a part to the open deck type cylinder block 1 of casting the cylinder liner 3, and is constituted so that the outer peripheral side of this MMC sleeve 4 faces a water jacket 12. Thus, strength of the deck surface 1a part is enhanced without making an aluminum alloy independently exist in the deck surface 1a part. Strength of the whole cylinder bore part is also enhanced by applying the MMC sleeve 4 to the whole outer peripheral surface of the cylinder liner 3.