This book constitutes the proceedings of the 27th International Conference on Big Data Analytics and Knowledge Discovery, DaWaK 2025, held in Bangkok, Thailand, during August 25&27, 2025. The 12 full and 14 short papers included in the proceedings were carefully reviewed and selected from 62 submissions. The proceedings also contain one keynote talk, one invited talk and one tutorial. The papers were organized in topical sections as follows: Data mining and knowledge discovery; sequential data analytics and recommendation systems; graph data processing and analytics; data management and indices; Large language Models (LLMs); and Neural Networks.