Increasing the thermal efficiency of the Rankine cycle by changing the thermodynamic characteristics of the working fluid of steam turbine plants by using the effect of a second-order phase transition under the targeted action of a magnetic field is considered. An analysis of experimental studies on the change in the physicochemical and thermodynamic characteristics of water under the influence of force fields is presented. The possible ranges of change in the specific heat capacity of water, volatility and hidden heat of vaporization are determined. Since an abrupt change in specific heat capacity occurs without heat supply or removal, it has been suggested that a second-order phase transition occurs at the first stage of the technological cycle after treatment with a force field, and a first-order phase transition occurs at the stage of vaporization. Numerical studies are performed for a specific simple reversible Rankine cycle with a change in heat capacity and hidden heat of vaporization. It is shown that even a small increase in the specific heat capacity only in the isobaric-isothermal process in front of the steam generator by 5% can lead to an increase in the thermal efficiency of the Rankine cycle by 1.3%. Areas for further directions of the research were selected. Unlike traditional methods for increasing the thermal efficiency of the cycle of steam turbine plants, the availability to use the proposed approach will not require significant costs and changes in the design of power plants.