© 2020 We have synthesized composite of magnesium-iron borates Mg2(X).Fe3(Y) (here; B2O5 = X and BO6 = Y), using a facile and single-step hydrothermal approach. Where, the synthesis of the composites can help not only to effectively utilize the properties of both i.e. magnesium borates (Mg2B2O5) and iron borates (Fe3BO6) in a single material but also making it thermodynamically more stable at higher temperatures as compared to the individual metallic borates. The as prepared heterostructured-composite was analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and thermal gravity analysis (TGA) to confirm the morphology, crystallinity, composition, and thermal stability. Further, the composite was explored as a catalyst in the construction of a biosensor where it showed an excellent electrocatalytic activity toward dopamine (DA) oxidation. This study offers a clue to design a borates-based composite to be explored as an efficient electrocatalyst in the application of biosensing field.