Mixed orthorhombic Sr_x doped α-Sb₂O₄ (x=2,4,8 and 10 wt. %) nanostructures (NS) were successfully synthesized by simple chemical precipitation method. Crystal structure, morphologies and microstructures of the as-synthesized Sr_x: α-Sb₂O₄ NS were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XRD displayed that the NS were extensively crystalized and crystallite size increases with increase in the concentration of Sr²⁺ ions. SEM revealed spherical like morphologies and grain size varies between ~ 88 nm to 110 nm. Red shift in the optical absorptivity and increase in the optical band gap (E_g) displayed in UV-visible spectra as the Sr concentration increases in
α-Sb₂O₄ NS. In Fourier transform infrared spectra (FT-IR), intensity of the characteristic peak Sb-OH gradually increases as Sr²⁺ dopant concentration increases in NS. Electrochemical performances of Sr_x: α-Sb₂O₄ (x =10 wt. %) NS exhibited specific capacitance of 890 F/g at a current density of 1 A/g in 6 M KOH solution. Sr_x: α-Sb₂O₄ NS showed cyclic retention of 88.95 %, long term cyclic stability up to 1000 cycles and excellent repeatability and reproducibility. Sr_x:α-Sb₂O₄ NS act as a promising electrode material for super capacitor and can be used in high energy storage device applications.