Purpose: The purpose of this research paper is to explore what factors that affect customer purchase decisions in the online environment, particularly after the COVID-19 pandemic in the case of Vietnamese customers. Research Design, Data and Methodology: To clarify which factor has the most significant impacts on online purchasing decision-making process, this study proposed a research model including factors such as customer trust, proposensity to trust, system assurance, the quality of website design, attitude, and customer satisfaction. This study collected the data via online survey. Data analysis was conducted by AMOS 25.0 using the Structural Equation Modeling (SEM) method. Result: The results of this study shows that the purchase decisions were positively affected by customers' attitude, satisfaction, trust, and the quality of websites design. Additionally, factors such as perceived size and reputation and system assurance, have impacts on buyers' trust, while the propensity to trust has no significant impact. Conclusion: This study provides managerial implications. The results provide which factors should be improved to foster trust, attitude, customer satisfaction, and purchase decision in the online environment. The results also provide managerial implication on marketing strategies how to enhance better relationships with customers and to consider environmental issues in the era of post COVID-19.