The research aims to investigate the impact levels of determinants on the loyalty of accountants to FDI firms underlying investment management in Thanglong Industrial Park in Hanoi, Vietnam. We conducted a questionnaire consisting of 31 observation variables with a 5-point Likert scale. Independent variables were measured from 1 “without effect” to 5 “strongly”. The method of data collection was done through the survey and subjects are accountants in FDI firms doing business in Thanglong Industrial Park in Hanoi. After checking the information on the votes, there are 120 questionnaires with full information for data entry and analysis, This study employs Cronbach‟s Alpha test, and regression model. The results show that seven determinants including Working environment, The characteristics of working; Training, promotion prospects and development; Income, Personal characteristic, Collective work together and The method of leading had positive relationships with the loyalty of accountants. Based on the findings, some recommendations are given related to such determinants to improve the loyalty of accountants of FDI firms in general and FDI firms in Thanglong Industrial Park in Hanoi in particular. With which, those firms can enhance performance, reduce financial strain, saving on investment in the recruiting process of new staff, increase profitability to ensure investment management.