Cellulose, a renewable and biodegradable polymer, can be converted into 2,3-dialdehyde cellulose (DAC) with increased reactivity for use in functional materials. DAC formation is commonly achieved using periodate oxidation under conventional heating, although this approach suffers from long reaction times and low energy efficiency. Microwave-assisted DAC formation has been developed, but generally involves long reaction times and high power; therefore, optimization of DAC synthesis under low-energy and short-time conditions has not been widely studied. This study synthesized DAC from microcrystalline cellulose (MCC) via low-energy microwave-assisted periodate oxidation, aimed at reducing energy consumption while preserving effective aldehyde group production. The results showed that DAC formation was achieved under all experimental conditions, with the optimal condition at 700 W for 1.5 h, yielding the highest aldehyde content of 77%, which was significantly higher than that obtained by conventional heating at the same reaction time. FTIR, XRD, and SEM analyses confirmed structural alterations of cellulose, while thermal analysis indicated reduced thermal stability accompanied by increased char residue, attributable to hemiacetal formation. This study demonstrates that low-energy microwave-assisted periodate oxidation is an efficient and sustainable approach for DAC synthesis and supports the development of advanced cellulosic materials using energy-efficient processes. © 2026 Wiley Periodicals LLC.