Introduction:Vitamin B-12 is an important nutrient that the body uses to serve as a cofactor in many main cell reactions. Cobalamin, in combination with folate, is necessary for DNA synthesis in cells that undergo rapid turnover, such as haematopoietic and enteric lining cells. Increased homocysteine, reduced methionine, and impaired tetrahydrofolate formation are the physiological effects of either of the above nutrient’s deficiency.1 Material and Methods: Quantitative research approach will be adopted in current research study, Non experimental descriptive research design will be used in this study. Research study for this study was Neurological OPD and hospitalize patient in Mahatma Gandhi Hospital, Jaipur. Sample size will be calculated with appropriate statistical method after pilot study and purposive sampling technique. 400 sample use for this study. Result: Prevalence of neurological disorder due to vitamin B-12 deficiency was13.75% of participant were have mild deficiency of neurological disorder due to vitamin B-12 Deficiency, 66.75% of participant were have moderate deficiency of neurological disorder due to vitamin B-12 Deficiency and 19.50% of participant were have severe deficiency of neurological disorder due to vitamin B-12 Deficiency. These findings caution against identification of patient suffering from vitamin B-12 deficiencies. Discussion: Present studies assess the prevalence and clinical spectrum of vitamin B-12 deficiency in a cohort of patient presenting with neurological disorders in tertiary care hospital of Rajasthan.”