A filtering method and apparatus improve resolution of an ultrasound image in an ultrasound imaging system. The filtering method includes the steps of obtaining magnitude of at least one lateral direction signal component among ultrasound filed characteristics which lowers resolution of an image, using Fourier transform, and scaling a signal focused in a mainlobe direction according to a ratio between the magnitude of the obtained lateral direction signal component and that of the signal focused in the mainlobe direction. The filtering apparatus includes a lateral direction signal calculator and a filtering unit.