A gear shift unit for an automated manual transmission, may include a shift block that is restricted in the rotational direction and slidably movable along a control shaft, and has a shift finger in order to implement a selecting operation with straight motion thereof and a shifting operation with rotation motion thereof, a driving actuator, a shifting unit selectively engaged with the driving actuator to rotate the control shaft by power of the driving actuator, wherein the shifting unit changes rotational direction of the control shaft in accordance with rotational angles of the driving actuator, and a selecting unit selectively engaged with the driving actuator to slide the shift block along the control shaft by power of the driving actuator while the shifting unit is not driven by the power of the driving actuator.