This book constitutes the refereed proceedings of the 20th International Conference on Information Security Practice and Experience, ISPEC 2025, held in Chengdu, China, during November 7–9, 2025. The 27 full papers and 8 short papers included in these volumes were carefully reviewed and selected from 72 submissions. They are organized in the following topical sections: Federated Learning; Cryptography and Security Protocols; Cybersecurity and Intrusion Detection; Multimedia Security and Side-Channel Attacks; Privacy Protection and AI Security.