The major aim of this paper is to explore the impact of Quality Management System on Product Quality in ISO Certified Large-Scale manufacturing firms in Kerala. Data for this study was collected using a Pre-tested questionnaire that was distributed to 60 ISO certified Large-Scale manufacturing firms ( 24 from public sector and 36 from private sector) in Kerala selected by purposive sampling method under non-random sampling technique from the database of Kerala State Industrial Development Council, Trivandrum. Two Top level managers (GM/MD/CEO's, DGM etc.) from the each firm were the respondent of the survey. 120 top level managers are selected for the study from both sectors (48 from public sector and 72 from private sector). Correlation analysis was used to analyze the collected data with the help of SPSS Software. The study reveals that there is a positive linear relationship between quality management system and product quality in ISO certified manufacturing firms in Kerala. This paper presents new data and empirical insights related with the relationship between quality management system and product quality in ISO certified Large-Scale manufacturing firm in Kerala.