A right looper release mechanism in an overlock sewing machine is disclosed comprising a vertically movable needle having a needle thread, a right looper disposed under the vertically movable needle and reciprocally movable in a direction crossing the vertically movable needle, a rear driving lever attached to the right looper and engaged in a right looper shaft so as to be freely turned relative thereto, a front driving lever fixed to the right looper shaft, a fixing screw member inserted in a throughhole of the front driving lever so as to be freely turned, said fixing screw member having a male screw being screwed into a female screw 3a of the rear driving lever so as to transmit a motion of the right looper shaft to the rear driving lever by way of the front driving lever, and an elastic member for elastically biasing the fixing screw member in a direction to release the fixing screw member so as to be unscrewed from the female screw of the rear driving lever.