This work deals with the ventilation optimization of the Kleinfeistritz mine in the municipality of Weißkirchen in Styria. The task of the work is to record the current status of the ventilation system in the Kleinfeistritz mine and to optimize it. For this purpose, a simulation model is used, which is calibrated by means of measurement results from the mine. The aim of this work is to be able to comply with the regulations for the gas limit values that will be valid from August 2023 and for this purpose different variants of the ventilation system are developed, analyzed and compared with each other. For the individual variants, we used ventilation doors, duct slides, other duct routing and enlarged dimensions of the ducts. These tools will be used to analyze the extent to which the ventilation system can be optimized. In order to record the current situation in the mine, all relevant data on the fan and the air ducts are collected at the beginning. For this purpose, pressure differences are measured at the fan and along the ventilation ducts. With this information and in combination with survey data of the underground mine workings, it is possible to transfer reality into a calculation model in the simulation software "VentSim". In order to be able to fully record the current status, gas concentrations ,air flows and pressure differences were measured. This model was used to simulate and compare different variants with modified ducting and weather routing. The results show that targeted ventilation routing improves the dilution of the resulting exhaust gases and significantly accelerates the ventilation of the blasting gases. In the event of a fire, the ventilation doors between the mining levels offer a further safety aspect, as they reduce the spread of gases in the mine workings, as shown by an exemplary simulation. The results of this work show that small changes to the ventilation system can be made to improve fresh air supply while saving costs. Another finding from this work is that the airflow in the slow fan stage is very much influenced by the moving machines and can change direction during operation. Furthermore, it was shown that the new gas limit values can also be complied with in the slow fan stage.