This thesis investigated the Mainland Chinese speakers’ performance on the Speaking Test of the International English Language Testing System (IELTS). It aimed to find out what language abilities the IELTS Speaking Test assesses and how well Chinese candidates perform on the test. More importantly, the thesis intended to identify the factors that influence Chinese candidates’ performance and the degree of importance of each factor. The data were collected through visiting IELTS training schools, observing simulated IELTS Speaking Test performance of Chinese candidates, distributing questionnaires, gathering documentation on the IELTS, and searching most recent and relevant information on the Internet. Data were analyzed through reduction, classification, calculation, comparison/contrast and examination of documents. The findings showed that the Speaking Test assesses communicative language ability of Chinese candidates, which was reflected by the daily common test topics, the format of a face-to-face interview, and the rating system which encourages the use of communication strategies. According to the average band score of the participants and their experience in answering interview questions, most participants were able to handle familiar situations but had difficulty in dealing with unfamiliar ones. It was also found that both linguistic factors, including vocabulary, pronunciation and grammar, and non-linguistic factors, including background knowledge, test instructions, L1 influence, test training, test anxiety, response time and test equipment, had some influence on the participants’ test performance. Of these 10 factors, vocabulary was found to be the most important one. For improved future performance on the IELTS Speaking Test by the Chinese candidates, recommendations were provided about teaching and learning of spoken English in Mainland China.