Abstract: Provided is a method for reducing methane production in animal stomachs by adding melatonin to gastric juice of the animal or feeding the animal with melatonin. In the method of the present disclosure, 10?7 mol/L to 10?3 mol/L of melatonin can reduce the methane production from the in vitro gastric fermentation fluid, feeding melatonin of 8.0 to 35.0 mg/kg/day can reduce the methane production from the animal respiration from day 7 of feeding melatonin. The method of the present disclosure can reduce greenhouse gas emissions of animals, control environmental pollution and realize low-carbon farming.