Many studies have confirmed the merits of metformin to treat type 2 diabetes, but few studies have addressed its effect on the respiratory system. Moreover, vascular endothelial growth factor (VEGF) is critical to many lung functions. In this way, we evaluated the metformin impact on the lung in treated obese Swiss mice, induced by postnatal overnutrition. Glucose and insulin were detected and the insulin resistance index (HOMA) was calculated; inflammatory cells and nitrite/nitrate concentration (NOx) was quantified from bronchoalveolar lavage, collagen and lung VEGF-a was analysed in the lung tissue and lung mechanics were evaluated by methacholine-induced bronchoconstriction. Values of glucose, insulin, HOMA; VEGF-a and collagen demonstrate the partial ability of metformin to improve the effects of obesity. However, metformin is ineffective in re-establishing the inflammation, shows no effects on NOx and does not restore bronchoconstriction in obese mice. In conclusion, metformińs beneficial effects on lung are questionable in the postnatal overnutrition model of obesity.