This research was conducted to investigate the impact of equity in foreign direct investment (FDI) firms on accountants' loyalty in Thanglong industrial park, Hanoi, Vietnam based on Equity theory. Da... ata were collected through a survey with 150 accountants from Thanglong industrial park. With this data, we have used Cronbach's Alpha, Exploratory Factor Analysis (EFA) and correlation analysis to determine the effects of the independent variables on the dependent variable, i.e. the loyalty of accountants. The results show that the equity in FDI firms had positive relationships with the loyalty of accountants in Thanglong industrial park. Based on this finding, this paper gives several recommendations for improvement the loyalty of accountants in Thanglong industrial park more