This work describes the importance of steam turbines and elaborates the first stage calculation of condensation steam turbine. The historical development of steam turbines is described, their industrial significance and usage. After analyzing the working principle of the steam turbine through its parts and conversion of energy through the process, the thermodynamical calculation of the first stage of the turbine was made. Given data, which were the basis of this calculation, are steam pressure at the beginning of the process 80 bar, the steam temperature at the beginning of the process 500°C, speed of rotation 130 min-1 and the steam temperature at the end of the process 0,05 bar. The steam turbine does not have regulated deduction and mass steam flow is 20 kg/s, while the effective force on the coupler is 12 MW. The results of the calculation are obtained parameters such as steam velocity triangle at the output, respectively at the input to stator and rotor grid. Based on these parameters, the profiles of stator and rotor blades were selected based on their characteristics, and then the number of the stage is calculated. As confirmation of the selected parameters, the control calculation of rotor blade dimensions was made and then the rotary blade of the first stage of the turbine was constructed with all its characteristic dimensions and defined profile. The attachment contains Mollier's h, s- diagram for water steam where is shown the steam expansion in the turbine, the plot of the longitudinal cross through the steam turbine and the plot of the rotary blade of the first stage.