The study compares three classification methods—fuzzy KNN, C4.5 algorithm, and Naïve Bayes classifier—for diagnosing diabetes mellitus using data from the UCI Pima database. Results indicate that fuzzy KNN is the most accurate with a maximum accuracy of 98%, followed by Naïve Bayes at 90%, and C4.5 at 86%. The research emphasizes the importance of early detection of diabetes to prevent complications.