Abstract: In order to investigate the function of Mfn2, isotopic tracer technique was used to measure the changes of fatty acid synthesis and hepatic glucose production in Mfn2 gene silencing mice mediated by RNA interference. Mfn2 shRNA and negative control plasmid were constructed by using shRNA target finder program. Twenty-four mice were randomly divided into transfection and control group. In transfection group, mice were injected with Mfn2 shRNA plasmid by vena caudalis; and in control group, mice were injected with negative control plasmid by vena caudalis. 5 days after injection， all mice were administered ³H-labeled glucose or ³H₂O by vena caudalis or intraperitoneal injection. Then blood and tissue samples were taken at specific times. Radioactivity was measured in all samples with liquid scintillation counter. The rates of hepatic glucose production and fatty acid synthesis in vivo were calculated. The rate of hepatic glucose production was significantly elevated in Mfn2 gene silencing mice (49.43±16.31), compared with negative control mice(24.91±4.07),P<0.05. The rates of fatty acid synthesis in liver, muscle, heart, and adipose tissue (0.10±0.00， 9.12±1.90， 1.18±0.28 and 11.11±1.31, respectively) in transfection group, were significantly lower than that in control group (0.79±0.07， 70.52±13.95， 53.88±990 and 45.43±5.91). 3H tracer study confirms that Mfn2 gene plays an important role in maintaining glucose and lipid homeostasis in vivo.