This book constitutes the refereed proceedings of the 43rd National Conference on Theoretical Computer Science, NCTCS 2025, held in Kunming, China, during August 3–5, 2025.The 9 full papers and 1 short paper included in this book were carefully reviewed and selected from 83 submissions. They were organized in topical sections as follows: Algorithm Design; Logic; Artificial Intelligence Theory and Algorithm; and Algorithm Application.