Preparation of green cellulose nanoparticles (CNPs) from renewable resources is becoming an important area of research. An agro-waste such as sesame husk has been used for the first time to generate cellulose nanoparticles. Sesame husk, which is deep brown in color, was treated with 0.7% sodium chlorite solution, followed by alkali treatment. This chemically treated mass was subjected to acid hydrolysis with 35% sulfuric acid. Cellulose microwhiskers were released from the husk, forming a white colloidal suspension and leaving a solid residue at the bottom. These microwhiskers were examined by optical microscopy and transmission electron microscopy (TEM). The microwhiskers were observed to be multifaceted, existing in associated form and having width in the range of 1-2 mu m. These microwhiskers were subjected to homogenization, after which spherical cellulose nanoparticles (CNPs) were produced having diameters in the range of 30-120 nm. X-ray diffraction study of these white cellulose nanoparticles and the residue showed a highly crystalline nature of the cellulose particles. Atomic force microscopy also confirmed the spherical shape of the cellulose nanoparticles. The block hardness and modulus of the CNPs were measured by nanoindentation tests.