Metformin (Met) is a drug developed for the treatment of patients with type Ⅱ diabetes. Recently, Met estimation in pharmaceutical formulations and human fluids has gained a growing interest. To extend requisite data that can be used to assessment of Met quantitatively based on charge-transfer (CT) complexation, the present study describes the synthesis and characterization of CT complexes that formed between drug Met and the organic π-acceptors picric acid (PA), chloranilic acid (CLA), chloranil (CHL), 7,7’,8,8’-tetracyanoquinodimethane (TCNQ), and dichlorodicyanobenzoquinone (DDQ). The properties of the formed CT complexes were investigated by elemental, spectral (UV-visible, IR, and Raman spectroscopies), thermal (TG) and morphological (SEM) studies. IR results indicated that the complexation of Met with either PA or CLA acceptors occurs through proton transfer interaction, whereas its complexation with CHL, TCNQ, or DDQ acceptors occurs through n→π* interaction.