Neurological disorders and diseases are on the rise in the world, while pharmacists are being encouraged to encapsulate drugs into the nanocarriers. The critical key question is which size of nanocarrier has a promising neurotherapeutic effect. In the present study, FTY-720, an FDA approved drug, was encapsulated into O/W nanocarriers. SEM and DLS data indicated in ultrasonication and stirring methods resulted in spherical nanocarriers with a particle size of 60 and 195 nm (nF60 and nF195), respectively. Further to investigate the effect of particle size on neuronal cells, MTT assay, PI flow-cytometry, LDH release, and NO production examinations were performed. Results showed that small nanocarriers increased cell viability along with the decline of dead cells, while both nanocarriers decreased LDH release and NO production as compared to the conventional drug. Notably, qRT-PCR and western blotting data related to apoptotic markers indicated in the increase of cell mortality in cells treated by nF190 was not due to the increase of apoptosis and Bax/Bcl2 ratio. It is worth mentioning that integrin α5 as a cell surface receptor involves in neuritogenesis was over-expressed in neuronal cells treated by small nanocarriers. However, nF60 increased PTK2 over-expression along with neurite outgrowth, as well. In other words, nanocarriers at the size of 60 nm are preferred to 195 nm as a drug carrier in neurotherapy due to profound impacts on neural cells. Thanks to small nanocarrier broad positive action on neural viability and neurite outgrowth. The present study discloses a pharmaceutical strategy to design drugs based on their particle size efficiency.