The condenser is a device for condensing steam from a turbine. Used steam from the turbine enters from the top of the condenser, then experiences condensation due to absorption of heat by injected cooling water. Condenser is one component that is very important in electricity generation. Lahendong Geothermal Power Plant has produced 4 × 20 MW of electricity. Condenser performance will affect the efficiency of a power plant and affecting the condenser is the heat transfer rate and the mass flow rate of the water in the condenser. this research is a correlation study between cooling towers and condensers, because one of the parameters used is condenser cooling water distributed by cooling towers. The calculation results show the highest heat transfer rate reaches 1327.53 Watt at water temperature 3.16 ℃ with the value of water mass flow rate 76.97 kg / s, while the lowest heat transfer rate value reaches 579.58 Watt at water temperature 1.38 ℃ with the value of water mass flow rate 40.09 kg / s. This means that the temperature of the cooling water is directly proportional to the heat transfer rate and the water flow rate of the condenser.