A portable terminal having a motion detection function and a motion detection method for the portable terminal are provided. A motion of the portable terminal is input by measuring an acceleration along the X-, Y- and Z-axes of the portable terminal. A current posture of the portable terminal is calculated by calculating rotation angles along the X- and Z-axes with respect to the X- and Z-axes in a basic posture using the acceleration along the X-, Y- and Z-axes. The acceleration along each axis is converted to an equivalent basic-posture acceleration along each axis using the rotation angles. The detected motion of the portable terminal is recognized using the basic-posture acceleration along each axis.