A micropower passive electronic lock cylinder including an immovable cylinder body (3), a rotatable plug (1), and an electronic control circuit part is described. An electronic control circuit board (13) electrically connected with a micromotor (14) and locating switches (15, 16) is arranged in the rotatable plug (1). A lock pin (8), which is controlled by a displacement limiting cam (5) driven by the micromotor (14), moves between the immovable cylinder body (3) and the rotatable plug (1) to release or block the rotatable plug (1).