Numerous studies have been carried out regarding different early and medieval writing bases like papyrus, birch bark, parchment, and Tālpātra. The quality of plant-derived manuscript writing bases has been aided by the presence of cellulose and lignin in plant cell walls. Sāncipāt, a popular writing base in early and medieval Assam, India, has not yet been thoroughly studied in this regard. In this paper, a scientific attempt has been made to reveal the physicochemical and mechanical properties of cellulose and lignin fibre in Sāncipāt. Various analytical techniques, including FTIR, P-XRD, TEM, UTM, were employed to characterize the cellulose fibres and lignin extracted from both old and new Sāncipāt, as well as their modified forms. A comparative analysis was made between the old and new bark samples of both cellulose fibres and lignin, and the general conclusions drawn from this work can be attributed to structural, thermal, and morphological changes of both cellulose fibres and lignin with degradation and decomposition, accompanied by ageing. The structural and chemical compositions of the extracted samples from the old and new barks were found to be almost identical, indicating only some minor degradation. While FTIR and UV spectroscopic analyses of the samples confirmed the successful extraction of cellulose fibres and lignin, electron microscopy and X-ray diffraction techniques allowed observing the structural and morphological changes that had occurred in the old bark samples as a result of ageing. Thermal stability studies and tensile strength measurements were also carried out to investigate the mechanical properties of the old and new bark samples.