This two-volume set, CCIS 2356 and CCIS 2357, constitutes the refereed proceedings of the 9th International Conference on Data Mining and Big Data, DMBD 2024, held in Ho Chi Minh City, Vietnam, in December 2024. The 46 full papers presented in these volumes were carefully reviewed and selected from 93 submissions. They are organized under the following topical sections: Part I : Machine Learning Methods; Data Mining Methods; Detection Methods. Part II : Clustering Methods; Knowledge Graph; UAV Applications; Large Languange Models and Applications; Multi-Criterion Models and Applications.