Construction labor productivity is an important aspect of a construction project. However, low productivity problems have had a significant impact on construction project timeframes resulting in over budget expenditure. The objective of this study was to determine the factors affecting labor productivity in Thai construction projects. A structured questionnaire survey was employed, completed by 54 executive managers from leading companies in Thailand. The five highest importance ranking factors affecting labor productivity were found to be: lack of workers, financial shortages, incomplete drawings, labor skill and experience, and incompetent construction management team. It is hoped that the results of this research will lead to improved productivity and effectively in project work. The study is an initial investigation about labor productivity and examines the improvements necessary to make the Thai construction industry more competitive and profitable.