In this thesis a closed-cycle gas turbine has been analyzed by using 5 different working mediums: carbon dioxide, helium, neon, argon and nitrogen. The analysis was firstly conducted with the turbocompressor and turbine at 90 % isentropic efficiency and later repeated with isentropic efficiencies varying from 80 % to 96 %. The input values at the beginning were: temperature at the entrance of the turbocompressor T1 = 32 °C = 305,15 K, temperature at the entrance of the turbine at T3 = 505 °C = 778,15 K and also the pressure at the same two places with values of p1 = 7,7 bar and p3 = 20 bar. The mass flow through the whole closed-cycle gas turbine was 𝑚̇ = 90 kg/s regardless which working medium was used. After calculating the missing operating parameters in each characteristic operating point of the process, it was necessary to calculate the power of the turbocompressor and turbine, delivered heat to the process and discharged heat from the process, useful power and efficiency of the whole process. At the end, the influence of each working medium on the operating parameters of the process showed how much it relied on different specific heat capacity values and isentropic efficiencies of the turbocompressor and turbine. The final results differed depending on the working medium and used parameters, showing for example that the useful power varies from 0,6 MW up to 41,74 MW. Also, the process efficiency differed a lot, from 2,82 % using carbon dioxide up to 27,52 % using helium and neon.