A cylinder block for an automotive internal combustion engine. The cylinder block comprises a cylinder block side wall which includes a boss section located corresponding to a position between adjacent cylinders and is formed with an oil dropping passage through which lubricating oil to be returned to a crank case is introduced. In this cylinder block, the oil dropping passage is located adjacent the boss section and includes an upper passage portion, a lower passage portion, and an intermediate passage portion connecting the upper and lower passage portions. The cylinder block side wall includes an outer wall surrounding the intermediate passage portion of the oil dropping passage. The outer wall has an axially extending side section located at one side in an engine cylinder row direction. The axially extending side section linearly integrally connects the lower end of the boss section and the lower deck.