PURPOSE: To provide a rubber blanket for offset printing which can be manufactured simply and at a low cost and is free from the generation of a loss in the print quality due to a vibration load caused by a cylindrical groove impact and further, whittle down a paper loss. CONSTITUTION: The rubber blanket is structured of a cut support plate 1 and a rubber layer 7 positioned appropriately to a printing width on the support plate. In addition, the starting extremity part and the ending extremity part of the support plate 1 and the starting extremity part and the ending extremity part of the rubber layer 7 are connected to each other respectively and the outer peripheral face of the rubber blanket is formed in a well-arranged manner without a gap. Further, the rubber blanket covers a rubber cylinder at a working position in such a manner that the former comes into frictional contact with the latter, acting as a sleeve and also is attachable to and detachable from the latter. Besides a positioning device 6 for determining a reproducible position is installed on at least one of the end faces 3, 5 of the rubber blanket.