Creativity is widely acknowledged and manifested a universal human experience, yet its definitions and assessments are complex and vary in different cultures. This paper aims at exploring the effect of English language ability on university students’ creativity assessment. With two studies, the investigation was conducted among students of English as a Second Language (ESL) and Native Speakers of English (NSE). Creativity assessment test Torrance Test of Creative Thinking (TTCT) was used in both a United States university class and a Chinese university class. The Alternative Use Test (ALT) and Remote Associates Test (RAT) were used in the US university class. All three tests are a widely used means to evaluate an individual’s creative ability. These tests require some degree of written text to communicate the creative concepts. The TTCT, ALT and RAT were used by US students in the first study. As hypothesized, the results indicated a significant difference in creative ability between ESL and NSE students, with NSE students’ scores being much higher than that of ESL students. Scores of TTCT revealed no strong correlation between self-rating of English ability and creativity. It was hypothesized that the language in which the test is taken is a critical factor. A second study was conducted among Chinese university students (ESL) with the TTCT. Approximately half of the students were given the TTCT in Mandarin; the other half was given the test in English. Disproving our hypothesis, there was no significant difference in creativity scores, showing that English ability was not a critical factor in the TTCT. However there is a significant difference when comparing TTCT scores of the Chinese students to that of the NSE students. This data suggests that Chinese students are likely less creative than NSE students as evaluated by the TTCT. Factors which affect the result of creativity assessment are various, of which language plays certain functions in the aspect of opening up individuals’ vision, inspiring their imagination and better understanding the works of art from other cultures. In the last part of this thesis, the author points out that when making a fair and reliable conclusion about individual’s creative ability, elements in social, cultural and educational diversities should certainly be included.