An apparatus and a method are configured for estimating a slope angle of a road. The slope angle of a road is estimated based on a longitudinal slope angle of the road which is calculated based on a Kinematic model, an effective weight corresponding to a control amount of a driver and a filter constant to estimate the slope angle of the road with higher precision in the case of a U-turn, rapid acceleration, or rapid deceleration in which a longitudinal acceleration of the vehicle is remarkably increased. The apparatus includes a controller to estimate the slope angle of the road, based on a longitudinal slope angle of the road which is calculated based on a Kinematic model, an effective weight corresponding to a control amount of a driver and a filter constant, and an output device to output the estimated slope angle of the road.