To measure the fuzziness of fuzzy sets, this paper introduces a distance-based and a fuzzy entropy- based measurements. Then these measurements are generalized to measure the fuzziness of fuzzy parti-tion, namely partition fuzziness. According to the re-lationship between the validity of fuzzy partition and its partition fuzziness, a family of cluster validity functions is proposed based on the modified partition fuzziness. The new cluster validity functions over-come the increasing tendency of the traditional parti-tion fuzziness with the cluster number, which pro-vides an effective analysis methodology for fuzzy cluster validity. The experimental results with dif-ferent testing data sets illustrate the effectiveness, reliability, sensitivity and applicability of the pro-posed cluster validity function.