Calcium oxide–doped bismuth nickel oxyhydroxide (CaO–BiNiOOH) nanostructures were successfully synthesized via a hydrothermal route. The obtained samples were characterized using XRD and FESEM analyses and subsequently employed for electrode fabrication in supercapacitor applications. The tailored morphology provides electrochemically active sites, enabling efficient charge transfer and storage. The fabricated electrode delivered a specific capacitance of 350 F g⁻¹ at 1 A g⁻¹ in 1 M KOH electrolyte, along with stable cycling performance. These findings highlight that CaO doping in BiNiOOH frameworks can effectively modulate electrochemical behavior, offering a pathway toward reliable energy storage devices