This book constitutes the refereed proceedings of the 6th International Conference on Big Data and Security, ICBDS 2025, held in Nanjing, China, during December 5–7, 2025. The 16 full papers and 1 short paper presented in this volume were carefully reviewed and selected from 250 submissions. They are grouped into the following topics: Big Data&New Method; Artificial Intelligence&Machine Learning Security; Data Technology&Network Security.