Abstract Accurate determination of molecular weight is crucial for understanding the chemical and physical properties of cellulose. However, traditional methods for analyzing high-molecular-weight cellulose are often unsuitable for cellulose oligomers. In this study, we emphasize how the molecular weight distribution affect the accuracy of four characterization methods, including liquid and solid-state nuclear magnetic resonance (NMR) spectroscopy, matrix assisted laser desorption/ionization mass spectroscopy (MALDI MS) and size exclusion chromatography (SEC). These techniques were compared on two typical cellulose oligomers with diverse molecular weight and properties. None of the techniques investigated could accurately characterize the molecular weight of cellulose oligomers with a broad molecular weight distribution. Liquid-state NMR was reliable method to determine the number-average molecular weight but do not give molecular weight distribution. MALDI MS was more sensitive to the low molecular weight portion, whereas SEC was a preferred technique for cellulose oligomers with relatively higher molecular weight. For solution-based characterization techniques, carbanilation was the prefered derivatization method over nitration due to its higher scattering power or increase of molar mass. MALDI MS revealed cellulose molecules had dissimilar degree of substitution through the same carbanilation reaction, which may explain errors in molecular weight determination by SEC. Overall, our study highlights the importance of considering molecular weight distribution when characterizing cellulose oligomers and demonstrates the strengths and limitations of different techniques for this purpose.