Research in English for Academic Purposes has begun to show that non-native speakers of English have much difficulty in English academic listening at American universities. Chinese students, who are from a very different educational system and cultural environment, experience special challenges in English academic listening. This paper focuses on how American professors' use of English in class affects Chinese students' understanding of academic lectures. Seventy-eight Chinese students who enrolled in the 2000 winter semester at an American university participated in this study. The results show that 1) the rapidness of professors' English speech; 2) professors' lack of clear pronunciation; 3) professors' use of long and complex sentences; 4) professors' use of colloquial and slang expressions; 5) professors' lack of clear definition of terms and concepts; and 6) professors' use of discourse markers affect Chinese students' English academic listening at an American university. It offers important suggestions for American professors as how to make their lectures more accessible to Chinese students.