Disturbances of microRNAs (miRs) expression or function play a role in several aspects of metabolism and glucose homeostasis. We have previously shown alterations in expression of miRs in insulin target tissues in the GK rat model of spontaneous type 2 diabetes, when com pared to normoglycaemic control strains. Investigations in our group in control mouse strains have demonstrated that high fat diet (HFD) feeding promotes the development of insulin resistance, obesity and fatty liver in 129S6 and C57BL6/J mice, whereas BALB/c are resistant to these experimentally induced phenotypes. The objective of the present work is to further study the implication of miRs in insulin resistance in two insulin target tissues (liver and adipose tissue) in these mouse strains. At five weeks, male mice of C57BL6/J, BALB/c and 129S6 were fed a normal carbohydrate diet (CHD) containing 5% fat, 19% protein, and 3.5% fibre or 40% HFD containing 32% lard oil and 8% corn oil ad libitum. At five months, liver and white adipose tissue were dissected (n=3-5), total RNA extracted and the expression of miR-125a, miR-27a, miR- 222 and miR-29a were determined using ABI’s taqman microRNA assays. 1/ When fed CHD, the expression of the four miRs was significantly higher in adipose tissue than in liver in the three mouse strains. Only miR- 29a showed lower expression (p<0.05) in adipose tissue than in liver in 129S6 mice. 2/ When fed CHD, expression of miRs were highly variable between the 3 strains in both liver and adipose tissue. 3/ In HFD-fed 129S6 mice, expression of both miR-125a and miR-27a was upregulated in both liver (x4.6, p<0.05 and x2.1) and adipose tissue (x2.5, p<0.05 and x1.3). Tissue-specific miR over-expression was observed in liver for MiR-222 (x3.4, p<0.05) and in adipose tissue for miR-29a (x1.5). 4/ In HFD-fed C57BL6/J mice, miR-125a expression was not altered neither in liver nor adipose tissue. In response to HFD, expression of miR-27a was increased in liver (x2.4) and decreased in adipose tissue (-2.3). MiR-222 was over-expressed in liver (x3.4, p<0.05) and not altered in adipose tissue. Expression of miR-29a was unaffected in liver and decreased in adipose tissue (-1.6). 5/ In HFD-fed BALB/c mice, expression of miR-125a and miR-222 was not altered neither in liver nor adipose tissue. Expression of miR-29a was unchanged in liver and increased in adipose tissue (x1.4). Expression of miR-27a was unchanged in liver, but decreased in adipose tissue (-1.6). Our results demonstrate the complex tissue- and strain-specific regulation of miRNA expression in experimentally induced insulin resistance, obesity and fatty liver disease. We observed a distinct correlation between miR altered expression and the metabolic status of HFD-fed mice. The 129S6 strain, very sensitive to HFD-induced glucose intolerance and obesity, exhibited miR over-expression in 75% of cases, whereas BALB/c, which is relatively resistant to HFD, showed miR altered expression in only 25% of cases. Our results provide strong evidence supporting a role of miR on impaired glucose homeostasis in models of spontaneous (GK) and experimentally induced (129S6) insulin resistance.