Nowadays, air transport is in an intense development phase. In order to optimize air communication and make it even more economical and environmentally friendly, attempts are made to undertake such activities as, e.g., SESAR project, which aims to develop and implement a modern ATM system. One of the parts of this project is the research on minimizing fuel consumption and emissions of pollu-tants in the engine exhausts. In the paper there is therefore presented the methodology for determining emission of those pollutants for the longest stage of the flight – the cruise phase. First, the value of the thrust required for the flight of an exemplary aircraft was deter-mined, and then the values of the engines trust and specific fuel consumption were computed. Additionally, it was necessary to determine the Emission Indexes (EI) of CO, NOx, HC and CO2 for the cruise phase, based on known such indexes for the LTO. Total emissions of these pollutants for the mission adopted to conduct research – a 1000 km long cruise – were determined. These emissions were computed for the exemplary aircraft per one kilometre, as well as per one hour of flight for various cruising altitudes and flight speeds.