This research was carried out in the Mexican manufacturing industry, the second most important activity in the country's industrial sector, specifically in the transportation equipment manufacturing subsector, which generates 19% of the jobs in this industry. Thus, it is important to develop improvement strategies to strengthen the sector's competitiveness. Currently, Lean Manufacturing projects are considered the most important strategy for manufacturing companies to achieve world-class performance. However, such projects yield different results, depending on the level of Critical Success Factor (CSFs) implementation during their development. This work proposes the design and validation of an instrument to evaluate the implementation of CSFs during the project-improvement phase in the production of transportation equipment in the Mexican manufacturing industry. The instrument is made up of six CSFs selected from the reviewed literature on Lean Manufacturing methodology and improvement projects and measured through 31 items. The instrument was verified and empirically validated through exploratory factor analysis, confirmatory factor analysis, and reliability analysis, using the SPSS Amos ® software program and a sample of 240 valid surveys applied to experienced developers of Lean Manufacturing improvement projects. The results show that the proposed instrument holds enough statistical validity to be used by the companies in the sector in order to assess the impact of critical success factors on the development of improvement projects. Additionally, the survey can help companies to identify areas of opportunity by adopting the Lean Manufacturing methodology and fit models, to assess the interaction of the FCEs in achieving the expected results of improvement projects. INDEX TERMS Critical success factors, lean manufacturing, confirmatory factor analysis, construct validation, mexican manufacturing industry, improvement projects.