<p>Cellulose, a natural material with considerable abundance, has recently garnered significant attention within the medical industry. In addition to its abundance in nature, cellulose possesses properties such as biodegradability and biocompatibility, which have the potential to be utilized in various medical fields, including the encapsulation of bioactive substances, tissue engineering, vaccine delivery, drug delivery, and gene delivery. Cellulose is composed of extended chains of glucose molecules that are interconnected by β-1,4-glycosidic bonds. The distinctive structural characteristics of cellulose, which enable its effective modification, have rendered it a valuable instrument in medical sciences and nanomedicine. This review presents the physicochemical properties and structural features of cellulose and systematically classifies cellulose nanoparticles, including cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), and other cellulose-derived nanostructures. We outlined for the synthesis of cellulose nanoparticles, encompassing microemulsion, self-assembly, ionotropic gelation, and surface modification. The following applications of cellulose nanoparticles are discussed: encapsulation, drug delivery, imaging, and gene delivery. The text also discusses current challenges and future perspectives for clinical translation and scalable biomedical applications.</p>