Provided is an improved pornography blocking technique which blocks pornography on the basis of the contents of multimedia data. First, feature descriptor is extracted from multimedia data inputted from the Internet by using MPEG-7 scheme. And referring to reference pornography database which stores reference pornography in the form of feature descriptor, the similarity degree between the extracted feature descriptor and the feature descriptor of the reference pornography is measured by calculating the vector distance between the two feature descriptors. And it is determined whether the inputted multimedia data is pornography or not, by comparing the measured similarity degree with the similarity measurement threshold value. According to the invention, accurate pornography determining is possible, because the invention uses the contents of the multimedia data for determining. And rapid and efficient pornography determining is possible, because the invention uses feature descriptor with less information, instead of the original multimedia data.