ABSTRACT Introduction: Schizophrenia and bipolar affective disorder are two major psychiatric illnesses, each affecting approximately 1% of the population. Schizophrenia is a primary psychotic disorder, affecting 20 million people worldwide. Bipolar disorder is a primary mood disorder, affects about 45 million people worldwide. Schizophrenia is a chronic debilitating mental disorder in which the person's emotions, thinking, judgment, and grasp of reality are so disturbed that his or her functioning is seriously impaired. Aims: To find out the comparison between schizophrenia and bipolar disorder on the basis of PET CT findings. Materials and Methods: The present study was a cross sectional, hospital based, single centered observational study. This Study was conducted from One Year (After approval from Health University & Institutional Ethics Committee) at Department of Psychiatry OPD in a tertiary care general hospital (NRS medical college & hospital, Kolkata, West Bengal). Result: We observed that In Bipolar Affective Disorder, 1 (2.8%) patient had Mild hypo metabolism and 35 (97.2%) patients had Normal Posterior Frontal Lobe Right. In Schizophrenia, all patients [36(100.0%)] had Normal Posterior Frontal Lobe Right and it was not statistically significant (p=0.3139). Conclusion: In Occipital Lobe Left, Diffuse hyper metabolism and Mild hyper metabolism were found in Bipolar disorder but Mild hypo metabolism and Mild to moderate hyper metabolism were found in Schizophrenia.