Glassy carbon (GC) electrode modified with Cu-based metal-organic frameworks (Cu-BTC, BTC = 1,3,5-benzenetricarboxylate) and multi-walled carbon nanotubes (CNTs) composites was developed. The Cu-BTCs were synthesized by two methods, traditional hydrothermal and ultrasonic irradiation methods. It was found that the Cu-BTC that was synthesized by the latter method, with mean crystallite sizes in the nanometers range, showed a higher impact on enhancing the electrocatalytic activity of the modified electrode toward the electro-oxidation of metformin compared to that synthesized with the former method with a larger crystallite size of micrometer-scale. The morphological characteristics of Cu-BTCs and Cu-BTC nanocrystals/CNTs modified GC electrode surface were characterized by scanning electron microscopy. The modified electrode showed excellent response of oxidation current for the determination of metformin. Under optimum conditions, the peak current showed good linearity with concentrations in the range of 0.5 µM to 25 µM and a detection limit of 0.12 µM, as well as good repeatability. The Cu-BTC nanocrystals/CNTs modified GC electrode was applied successfully to determine metformin in pharmaceutical samples with good accuracy. KEYWORDSMetal-organic framework, carbon nanotube, modified glassy carbon electrode, metformin, electroanalytical determination.