The micro-scale milling process is suitable for the machining of micro-scale three-dimensional shapes and is particularly effective for the machining of micro-channels and grooved patterns. Tools should be changed at an appropriate point in time to maintain high quality of machined surfaces and to improve productivity. Moreover, machining conditions that are optimized in terms of the tool life are required for the efficient use of micro-milling tools. In this paper, we propose a method for predicting the tool life of a micro-milling tool and establishing optimal machining conditions. Machining conditions are determined using a central composite design. An equation is derived for the tool life, and the effect of variables on the tool life is evaluated by carrying out a regression analysis on experimental results. Genetic algorithm is used to determine optimal machining conditions. The results of this study can be used to enhance machining efficiency in micro-scale milling processes.