Original scientific paperCellulose nanocrystals (SN) were isolated from the shell of horse chestnut seed using sulfuric acid hydrolysis. The raw shells were broken into small pieces, treated alkali, bleached, and subjected to the sulphuric acid process. The effect of hydrolysis time on the structure, crystallinity, thermal properties, morphology, and topology of cellulose and SNs were investigated. The lignin and hemicellulose contents were almost entirely removed from the produced cellulose through the alkali and bleaching treatments demonstrated to Fourier transform infrared spectroscopy (FTIR). The crystallinity of SNs was increased firstly with increasing reaction time and then along with the reaction times longer than 20 min. decreases. The optimal isolation time for SN production was found to be 20 min at 45 °C in a 50 % sulfuric acid solution. The morphology of the cellulose and SN were investigated by scanning electron microscopy (SEM) and revealed a changed needle-like surface structure of SN relative to cellulose. The surface roughness of cellulose with a Ra value of 585 nm is higher than the cellulose nanocrystalline with a Ra value of 111 nm, which were characterized using atomic force microscopy (AFM). The thermal stability of SNs was decreased during increased extraction times compared with cellulose.