A method and apparatus for generating discriminant functions for distinguishing obscene videos by using visual features of video data, and a method and apparatus for determining whether videos are obscene by using the generated discriminant functions, are provided. The method of generating discriminant functions includes: creating a first frame set by extracting a predetermined number of frames for each video data unit from a group of video data classified as obscene or non-obscene, and creating a second frame set by selecting the frames; generating a frame based discriminant function by extracting visual features of frames of the second frame set, and then generating a first discriminant value by determining whether each frame of the first frame set contains obscene video data; generating a group frame based discriminant function by extracting visual features of a group of frames of the first frame set, and then generating a second discriminant value by determining whether the frames of the group contain obscene video data; and generating a synthetic discriminant function by using the first and second discriminant values as a representative value of the video data. Accordingly, obscene video data stored in a computer system can be automatically and accurately distinguished.