This book constitutes the refereed post-proceedings of the 7th International Conference on Mobile Internet Security, Mobi Sec 2023, held in Okinawa, Japan, in December 19-21, 2023.The 21 full papers presented were carefully reviewed and selected from 70 submissions. The papers are organized in the following topical sections: 5G and 6G security; cryptography; machine learning-based security; identification and authentication; network design and security.