With the development of online shopping, the number of third-party online payment systems increases. Alipay is a commonly used third-party online payment system among Chinese consumers. The purpose of this study was to explore the factors that affect the users’ acceptance of Alipay among Chinese B2C customers. This study adopts a deductive, theory testing approach. Based on the model of Unified Theory of Acceptance and Use of Technology (UTAUT), a research model and hypotheses were proposed. A survey study was performed with a quota sample of 300 Chinese online shopping consumers. Based on the responses, the hypotheses were tested through statistical analysis. Through testing the hypotheses, it was concluded that: “Social Influence”, “Effort expectancy” were the factors that most prominently could affect B2C user’s acceptance of Alipay. Hence, third-party online systems suppliers should focus on social marketing and increasing the ease of use of the systems to increase user acceptance. Other similar third-party online payment company could take those identified factors as reference in further user acceptance study, and the proposed research model in this study could also help in improving understanding of user acceptance in similar third-part online payment system.