Plasma is the fluid in the body's blood. It contains proteins and other substances that are important for overall health. Plasma transfers are used for patients with liver failure, serious infections, and severe burns. The blood contains proteins called antibodies that can be developed by the immune system of recovered COVID-19 patients to fight the SARS-CoV-2 virus. The application of convalescent plasma was successful in the Spanish flu outbreaks in 1918. Subsequently, the success of applying convalescent plasma has also been found during the SARS epidemic of 2003, the influenza pandemic of 2009, and the latest Ebola epidemic in 2014. Currently, convalescent plasma therapy is in use for the COVID-19 epidemic. The hundred-year-old convalescent plasma therapy has been reported to reduce the mortality rate of coronavirus infections in Iran by 40%. This article can be a source of useful information about plasma therapy being used successfully for the treatment of COVID-19 infected patients worldwide.