A surgical fastener applier for receiving a power pack and a loadable power pack. The surgical fastener applier includes a housing containing a compartment, an elongated member extending distally from the housing, first and second jaws and a firing mechanism positioned within the housing. The firing mechanism is movable between a first position and a second position to effect firing of fasteners into the tissue clamped between the first and second jaws. A cover on the housing is openable to access the compartment. A power pack is removably loadable into the compartment, the power pack having a motor and an engagement member removably engageable with the firing mechanism within the compartment when the power pack is loaded into the compartment to effect movement of the firing mechanism from the first position to the second position.