Process of joining European Union implies adapting to new business conditions and improving the competitiveness of Serbian companies in order to be able to compete on equal terms in the European market. Implementation of quality management systems in manufacturing organizations is a significant advantage and it is one of the prerequisites for successful competition in open markets. In addition, implementation of ISO standards enables optimization of work processes and enhances competitiveness by resources optimization. This study, based on The European Manufacturing Survey (EMS) questionnaire, analyses competitiveness of Serbian companies through implementation of ISO 9001. The study has shown notable difference between certified and non-certified organizations in perception that product quality is the most important competitiveness factor.