The present work studied the possibility of using phthalimide for surface modification of cellulose nanofibers (CNF). The modification was carried out in 96/4 (v/v) water/acetic acid with CNF to phthalimide ratio of 1:0, 1:0.5, 1:1, and 1:1.5 wt%, respectively. Morphological, physical, chemical, and thermal properties of prepared aerogels were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction spectroscopy, and thermogravimetric analysis. The mechanical characterization such as the stress‐strain behavior was measured by compression testing. The results showed that surface modification and addition of phthalimide increased the surface area and pore volume but decreased the overall pores size. The presence of phthalimide onto CNF was confirmed by attenuated total reflectance‐Fourier transform infrared spectroscopy as the characteristic peaks of NH2, CN, and ester bonding ( COO−) appeared. Since more energy is needed for breaking hydroxyl bonds than ionic bonds, by taking into account the reduced hydrogen bonds as the result of the chemical modification, the thermal stability of the CNF‐Ph is lower than the pure CNF aerogel. Besides, the modulus of elasticity increased that could be due to the high densities.