This article investigates the post-mortem redistribution pattern of metformin in rats. Twenty-one rats were randomly divided into 7 groups, with 1 group serving as the control group and the remaining 6 groups as the experimental group. The experimental group rats were gavaged with 1 mg/kg metformin, while the control group rats were gavaged with the same dose of physiological saline. After 2 hours, they were euthanized and placed in a right supine position at room temperature (15℃). Heart blood, heart, liver, spleen, lung, kidney, brain, testes, and muscles were collected at 0, 6, 12, 24, 48, and 72 h after death. The metformin content in each tissue and organ was extracted using protein precipitation method and detected by liquid chromatography-mass spectrometry. This study found that the distribution of metformin content in various time points, tissues and organs of rats showed different patterns. Metformin exhibits post-mortem redistribution in rats after gavage, therefore, the heart, muscle, and lungs are suitable samples for forensic identification of drug concentration at the time of death.