Abstract: The objective of this study is to investigate the relationships among lean production, operational performance and firm performance; thereby, the study was conducted and accomplished by means of quantitative method using random sampling and snowball sampling. The results were analyzed by descriptive statistics, confirmatory factor analysis and the structural equation modeling by using statistical software programs. Considering the quantitative approach, a survey was conducted with 629 current middle and top managers working in Thai Manufacturing Industry. The majority of respondents were male (56.3%) of the age above 40 years old (32.6%), factory/production manager (39.1%), bachelor’s degree (75.8%), working in medium size company (36.9%), nonautomotive (60.9%) and company age above 15 years (46.6%). The findings reported that, there were positive relationships between lean production and operational performance, lean production and financial performance and operational performance and financial performance. In addition, the results presented that there was partial effect of lean production on financial performance through operational performance. Considering the structural model level, the results further revealed that the model was not different across the automotive and nonautomotive industry and the model was not different across the lean production adoption <5 years and above 5 years. Regarding the path level, the results reported that all of each path model level was not different across automotive and nonautomotive industry. Similarly, the lean production adoption whether <5 years or above 5 years did not have any effect on all of the path model levels.