In this paper the influence of product innovation and development on business performance and competitiveness in small and medium-sized manufacturing enterprises is addressed. The research was conducted via survey and it included over 2200 manufacturing enterprises from Serbia. The number of returned and usable surveys was 132 (5.98% return rate). The regression model included product development and innovation as two important engineering endeavours and business performance and competitiveness. Additionally, product quality, quality management system (QMS) and human resource management (HRM) were included in the data analysis. The results indicate that the observed relationships between the measured constructs are different, and they depend on how many employees the enterprise has. This paper contributes to the existing body of literature, provides a solid basis for future research in this domain, and other researchers and managers can use this paper as an insight to the relationships between important business metrics.