Ai Ssu-ch'i is a little known but very important figure in the introduction of Marxism-Leninism into China. This first article provides a brief biography of Ai Ssu-ch'i as well as a detailed account of his activities as teacher, author and propagandist. Among his other services to the cause of Marxism-Leninism in China, one has to stress Ai Ssu-ch'i's systematic opposition to Yeh Ch'ing and to the non-Communist interpretation of Dr. Sun Yat-sen's Three Principles of the People. (cf.SST 10 (1970), 138–166.).