An mmode imaging method and apparatus for an ultrasonic diagnostic device is provided to increase the continuity of displayed mmode images. An mmode imaging method performed by an ultrasonic diagnosis device selects sample points on frames of bmode images, converts bmode data of the sample points obtained from the frames of bmode images into converted mmode data, produces interpolated mmode data based on the echo data of corresponding sample points on at least two different frames, and images at least a portion of the mmode data in time sequence.