A de-interlacing device capable of de-interlacing a video field adaptively and associated method, the device includes a video field detector for detecting a video field and for outputting a motion detection parameter, a motion detector for detecting a motion difference between the video frame and at least one video frame neighboring the video frame, and for determining a motion ratio for the motion difference according to the motion detection parameter, and a de-interlacing unit for de-interlacing the video field according to the motion ratio output from the motion detector.