The aim of this final work is to examine measures and devices for reducing emissions of harmful substances from marine propulsion plants. The past has proved that mankind did not even know that there were harmful substances from the exhaust gases of propulsion plants, and when it finally came to an end, industry and progress were placed in the first place instead of concern for health and the environment. Today, when the world is familiar with the atmosphere, global warming, and when there is more attention for human health, there is a growing interest in both responsible and public for this problem. The main pollutants are carbon monoxide, nitrogen oxides, sulfur oxide, ozone and floating particles. Given that the Republic of Croatia as a full member of the European Union is obliged to align its laws with those European, legal regulations of Croatia regarding the limitation of these harmful substances are strict and in accordance with European law. There are international conventions to combat emissions of harmful gases, and the example of such a convention is MARPOL, in particular Annex VI to the aforementioned convention dealing with exhaust gases from ship propulsion plants. Many seas and bays fall under the ECA zone, and since they require low emissions of these gases, they contribute to environmental protection. Technology offers us solutions to reduce these emissions so today there are many exhaust gas purifying devices.