Vitamin B12 is one of the most essential vitamins affecting various systems of the body. Cases of neuropsychiatry disorders due to its deficiency are more common in elderly patients with prevalence of 10–20%. The most common psychiatry symptoms reported in the literature associated with vitamin B12 deficiency was depression, mania, psychotic symptoms, cognitive impairment and delirium. Here, we report a case of vitamin B12 deficiency in a 52-year-old male who presented with psychotic features: persecutory delusions, tactile and auditory hallucinations. Patient had neither recorded psychiatry history nor any drug abuse. Medical history includes hypertension, diabetes mellitus and glaucoma. The patient was not a vegetarian. All relevant laboratory evaluations and head CT were normal except vitamin B12. The patient was treated with antipsychotics (risperidone 3 mg/day) and intramuscular vitamin B12. One week after, there was total remission of psychotic symptoms. In the follow-up during the next four months, psychiatry symptoms did not recur at any time. This case reports a rare case of vitamin B12 deficiency induced psychosis. Although there was concurrent administration of an antipsychotic along with vitamin B12, it underlines the importation of evaluation of vitamin B12 and other potential reversible causes of psychosis.