PURPOSE: Tax compliance is a topic of concern for many scholars all over the world. Most of them point out factors affecting tax compliance, and one significant factor is the adoption of tax compliance. However, there have not been many studies analyzing the relationship between attitude towards an e-tax system, adoption of an e-tax system, and tax compliance. This paper aims to investigate the mediating impact of adoption of an e-tax system in the association between attitude towards an e-tax system and tax compliance based on empirical evidence from Vietnamese enterprises. METHODOLOGY: On the basis of the Theory of Reasoned Action (TRA), the research model is proposed. Accordingly, hypotheses are developed and this study applies a quantitative analysis with a research sample of 435 Vietnamese enterprises. The questionnaire includes close-ended questions sent to managers or tax accounting officers at enterprises by three methods: directly interviewing, via e-mail, and via the General Department of Taxation. The collected data are then processed and analyzed by SPSS v.22 and AMOS. The study applies Cronbach’s Alpha as a tool for assessing the reliability or internal consistency of scales. Following is the exploratory factor analysis (EFA). Finally, regression analysis is used to evaluate the impact of the independent variables on the dependent variable and to estimate the research model. FINDINGS: There are significant direct effects of the two independent variables, attitude towards an e-tax system and adoption of an e-tax system, with the dependent variable tax compliance. Furthermore, the adoption of an e-tax system partially mediates the association between attitude towards an e-tax system and tax compliance. This mediating effect positively consolidates the impact of attitude towards an e-tax system and tax compliance. IMPLICATIONS: This paper mainly focuses on the tax compliance of Vietnamese enterprises that could be further studied with foreign enterprises that have been operating in Vietnam. Besides, the research is conducted in the context of Vietnam, thus, it is a reference for studies in other developing countries having a similar economy or tax administration. ORIGINALITY/VALUE: This study contributes to enhancing research associated with tax compliance, especially investigating the mediating impact of adoption of an e-tax system in the association between attitude towards an e-tax system and tax compliance of enterprises in the context of Vietnam. The findings of the study suggest some policy implications for improving tax compliance in Vietnam including (1) continuously improving the information technology infrastructure for both tax authorities and enterprises; (2) widely disseminating tax law and providing support services to enterprises; (3) upgrading the e-tax system to ensure the effective coordination between tax authorities, tax officials, enterprises, and other authorities in applying e-tax; (4) consolidating the supervision and assessment of the adoption of e-tax; (5) promoting information and education on the perception of complying with the tax law for taxpayers in particular and the entire population in general; (6) developing a tax administration strategy based on tax compliance.