Metformin is an antidiabetic drug. It is used for the treatment of non-insulin-dependent diabetes. It has a low bioavailability and many side effects associated with oral application such as gastric irritation. In this study, non-ionic surfactants were used to produce and characterize seven microemulsions (MEs) containing Metformin HCL for oral and transdermal application. The MEs were characterized regarding their droplet size, poly disparity index, rheological properties, the flux through rat's skin, and in vivo bioavailability in rats. The results showed that MEs had colloidal properties. The droplet size was below 100 nm and the MEs had ideal viscosity (Newtonian viscosity). Besides, the in vitro bioavailability using Franz diffusion cells through the skin over 24 h showed a flux as high as 0.08178 mg/cm2.hr. Moreover, the oral in vivo and transdermal bioavailability in rats was higher than of the oral solution. The developed formulations are nonionic loaded metformin can be an ideal carrier and promising formulations for transdermal administration of Metformin HCL.