Objective It is well known that mitochondrial dysfunction might play an important role in the pathophysiology of insulin resistance. And recently, several studies suggest that celecoxib, one of COX-2-selective inhibitors, has positive effect on insulin sensitivity. Here, we investigate the effect of celecoxib on insulin sensitivity and mitochondrial biogenesis in in-vivo and in-vitro studies. Methods Twenty-week-old male OLEFT rats (n = 20) were separated into two groups: high fat diet fed and vehicle treated (n = 10); high fat diet fed and celecoxib (15 mg/kg) treated. Lean nondiabetic LETO rats were used as control. C2C12 myotubes were incubated in high palmitate condition (500 uM) with or without various doses of celecoxib (1, 3, 10, 30, and 50 uM) for 24 and 48 hours. To assess the mitochondrial biogenesis, nuclear peroxisome proliferator-activated receptor gamma coactivator-1a (PGC-1a), mitochondrial transcription factor A (Tfam), and nuclear respiratory factor-1 (Nrf1) expression were assessed by immunoblot. Results Five-week treatment with celecoxib did not change body weight, food intake, and fasting plasma glucose level. However, celecoxib improved insulin sensitivity in high fat diet-fed OLEFT rats in OGTT. Electron microscopic findings of gastrocnemius muscle and mtDNA/nuclear DNA showed that celecoxib preserved mitochondrial density in diabetic rat muscle. In in-vitro studies, celecoxib increased nuclear PGC-1a expression in a dose- and time-dependent manner. High dose palmitate treatment decreased nuclear PGC-1a expression, however, simultaneous treatment with celecoxib preserved nuclear PGC-1a expression. Regarding Tfam and Nrf1, there were no differences. Conclusion In summary, we have observed that celecoxib preserves mitochondria density and improves mitochondrial biogenesis in skeletal muscle in high fat diet-fed rats and palmitate-induced insulin resistance in C2C12 skeletal muscle cells.