This paper aimed to evaluate the factors affecting quality management (QM) through the quality management system according to ISO 9001 standards of Vietnam businesses. The authors surveyed on 200 manufacturing and technology enterprises that apply ISO 9001 quality management in Hanoi and Da Nang and HCMC. Factors affecting the effectiveness of quality management under ISO 9001 include five elements: (1) Management commitment; (2) Staff involvement; (3) Cooperation of customers and suppliers; (4) Consultants; and (5) Quality management document system. Research results show that the above factors had positive impacts on the effectiveness of the quality management system (QMS). The study has given a number of solutions for businesses that have been and will apply QMS in accordance with ISO 9001 with appropriate adjustments to promote the efficiency of the system.