One of the main challenges that developing countries face is the need to increase productivity. In Chile, the most important productivity gap in both mining and construction industries is the lack of operational efficiency, caused mainly by the low adoption of advance management methods. Hence, considering the need to increase productivity through operational efficiency, lean production emerges as a management system with the objective to create value while eliminating waste, and continuously seek operational excellence. This research evaluates the impacts of the implementation of lean methods in an underground mining development project in the execution phase, which will help to better understand to what extent these methodologies can affect the performance of this type of projects. This research indicates that the implementation of lean methods in an underground mining development project had a statistical significant improvement of the mean for all indicators studied. Likewise, the implementation produced a statistically significant reduction of the variability for some indicators; moreover, there is a considerable reduction in the coefficient of variation (CV), which indicates more stable processes. In addition, this research demonstrates that there is a statistically significant correlation between the percent of plan completed and its coefficient of variation.