Nowadays, the benefits of ISO 14001:2015 abound, for minimizing environmental footprints, providing operational improvements, bringing lucrative business and improving the company’s image. There is an annual audit to decide if the company’s environmental management system meets the requirements of ISO 14001:2015. This is a significant audit that strongly affects the current certificate. The study to “Evaluate the efficiency of the environmental management system ISO 14001:2015 at the Vietnam Onamba Company” has been conducted to research the internal audit and examine any discordance in the environmental management system. The study carries out the internal audit of the environmental management system ISO 14001:2015 at VTO company by 3P method (P1: Paper check, P2: People interview, P3: Practice Observe). The result of the study showed a minor discordance at (6.2) Environmental Objectives and planning to achieve them. Regarding other clauses, they meet the requirements of the environmental management system. The result shows that the responsibility and careful observation of the company in controlling the system. The study evaluates reducing consumption (electricity, water, and chemicals) through collecting and comparing the data between 2017 and 2018. The results show the efficiency of reducing consumption: monthly electricity consumption reduced 21,86% (377 MWh); monthly water usage reduced 17,89% (1421 m3 ); annual chemical usage reduced from 3 to 6%.