Thin film-based micro-supercapacitors have great potential for energy storage application in portable electronics, microelectronics devices and microelectromechanical systems. Nanocomposites of transition metal oxides and carbon materials are preferable for electrode materials in electrochemical capacitors due to the combination of high capacitance and long cycle life. However, the cost-efficient manufacturing of nanocomposites thin film for integration with silicon has been a significant challenge for commercialization. Herein we report a novel approach to rapid (~80s) pulsed photoinitiated synthesis of iron oxides-reduced graphitic oxides in-situ nanocomposite thin film on nickel-coated silicon substrate through pulsed white light irradiation of photosensitive iron-organic precursor made by chemical solution deposition. The instantaneous photoinitiated pyrolysis of photosensitive precursor occurs in the first couple pulses of irradiation and results in iron oxides-graphitic oxides composite thin film with a 3-D nanostructure. Subsequent pulsed light irradiation improves the crystalline quality of iron oxides nanograins and leads to the reduction of graphitic oxides. The nanocomposite thin film with a thickness about 1 um shows a high performance in 2M KOH electrolyte measured in a three-electrode cell. The unoptimized specific areal capacity by discharge is as high as 100 mF/cm² at 5 mA/cm² within the potential range from -0.8 to -0.25 V after stable cycling more than 5,000 times. This straightforward and scalable nanotechnology opens a new pathway to the manufacturing and practical application of iron oxides-reduced graphitic oxides nanocomposite thin films as anode materials in silicon-based micro-supercapacitor for microelectronics devices and microelectromechanical systems.