The purposes of this thesis were: (1) to explore the lexical and conceptual representations of Chinese-English bilingual university students, namely, to test the ´concept-mediation hypothesis´ and the ´word-association hypothesis´; (2) to compare the patterns of lexical and conceptual representations of bilingual university students with different levels of English proficiency, namely, to test the ´intermediate hypothesis´; (3) to compare the ´subtraction method´ paradigm and the ´semantic/associative priming´ paradigm in testing the above hypotheses. Twenty English non-proficient subjects participated in experiment 1. They were required to perform in two kinds of tasks: Chinese words translating, pictures naming (in English), and words and pictures categorizing (in Chinese). The subtraction method paradigm was used. The results showed that the reaction time difference between words tranlating and pictures naming is significantly smaller than that of words categorizing and pictures categorizing. These results supported the prediction of ´word-association hypothesis´. In experiment 2,twenty English proficient subjects were asked to perform in the same tasks as in experiment 1.The results were in line with those of experiment 1,also supporting the prediction of ´word-association hypothesis´. Twenty-four subjects participated in experiment 3, adopting the ´semantic/associative priming´ paradigm along with lexical decision task. The results showed that the priming effects were not significant when Chinese target words were used. However, the priming effects were significant when English words were used as target words. Since ´between-language repetition effect´ was equal to ´within-language semantic/associative priming effect´, and both were greater than ´between-language semantic/associative priming effect´, the prediction of ´word-association hypothesis´ was again supported.