Molecular weight information is essential for comprehending the chemical and physical properties of cellulose. However, traditional methods used to analyze high-molecular-weight cellulose are often unsuitable for cellulose oligomers. In this study, we emphasize the influence of molecular weight distribution on the determination of molecular weight using four characterization methods: liquid and solid-state nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), and size exclusion chromatography (SEC). These techniques were compared using two cellulose oligomer fractions with different molecular weight distributions. Liquid-state NMR was a reliable method for determining the number-average molecular weight but did not provide information on the molecular weight distribution. MALDI MS was more sensitive to the low molecular weight range, while SEC was a preferred technique for cellulose oligomers with relatively higher molecular weight. Among the solution-based characterization techniques, carbanilation was the preferred derivatization method over nitration for its higher scattering power and the increase in molar mass. MALDI MS revealed that cellulose molecules exhibited different degrees of substitution through the same carbanilation reaction, which may explain errors in molecular weight determination by SEC. 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.