A lock cylinder includes a cylinder housing with a upper pin hole set and a replacing opening, a cylinder body with a lower pin hole set, a upper locking pin set, a second locking pin set and a clip member. The cylinder body is movably disposed inside the cylinder housing. The upper locking pin set is disposed inside the upper pin hole set for engaging the cylinder housing and the cylinder body. The second locking pin set is disposed inside the lower pin hole set for disengaging the cylinder housing from the cylinder body. The clip member constrains the cylinder body from sliding on the cylinder housing in a first position, and does not constrains the cylinder body from sliding on the cylinder housing in a second position. The cylinder body slides to a replacing position for replacing the second locking pin set via the replacing opening.