<p>In last decade, organic Rankine cycle is proposed as an efficient application to convert low grade heat energy to electricity. Nowadays, n-pentane is widely used in geothermal power cycles. However the idea of using alternative fluids in Low Grade Organic Rankine Cycles (ORC) has gained due to the safety class of n-pentane (A3).<br />In this study, R1233zd(E) and HFO1336mzz(Z) were selected as the working fluids due to their safety properties. R1233zd(E) has A1 safety class and HFO1336mzz(Z) is non-flammable. Thermodynamic analyses were made for these fluids in ORC at the same working conditions. Analysis solution was made with EES (Engineering Equation Solver) software. Results were presented with graphics and tables. A comparison was presented in the point of view efficiency and safety.</p>