Abstract: A gear train locking mechanism for preventing the reciprocating slide of a mechanical power press from inadvertently moving during maintenance procedures and the like is disclosed. The gear train locking mechanism preferably includes an idler gear which is enmeshed with a drive gear of the power press and a movable arm assembly positioned for selectively engaging the idler gear to prevent its rotation. The engagement of the arm assembly and the idler gear effectively locks the gear train of the power press thereby preventing the slide of the power press from moving once the locking mechanism is activated.