Blood Transfusion Warmer with a high degree of accuracy and rapid temperature heating response is needed when going or doing a blood transfusion. This is very necessary so that the handling of blood transfusion cases can be done properly and to prevent the risk of danger due to inaccurate devices or low response speeds to heating. Failure in the process of blood transfusion can cause death in humans, one of the factors is that the blood temperature is too high or too low when the blood transfusion process can cause blood to become clotted or damaged. In addition, in the market, Blood Transfusion Warmer with high quality requires relatively large electrical power so that some people complain about the use of this tool. The purpose of this study is to optimize the heat energy generated through the heating component of the Blood Transfusion Warmer so that the temperature rise can take place faster, so it is expected to save time and save electricity usage. In this study, optimization has been carried out by heating the blood bag in a closed room made of acrylic with a thickness of 3 mm. The heater component used in this study is the Peltier. This heating component is controlled by using a microcontroller through the heater driver based on the input signal obtained from the temperature sensor, in this case using a temperature sensor with the name DS18B20. Barkey Blood Transfusion Warmer is used as a comparison tool because this tool has been widely used, especially in Indonesia. Based on the results of testing the equipment that has been done, the average difference in the results of reading the temperature value on the Blood Transfusion Warmer using a DS18B20 temperature sensor against a temperature calibrator with the name Lutron TM-902C that is equal to 0.2 °C. The maximum power used in the Blood Transfusion Warmer in this study is 187.75 watts.