Japanese encephalitis caused by infection with JE virus is one of the important cause of Acute Encephalitis Syndrome(AES), not only in various parts of India but also the North east of India . It is associated with considerable morbidity and mortality. The present study was done to determine the sero-prevalence of JE in the southern part of Assam and adjoining states, demographic profile of JE amongst the population, clinical profile of the JE positive cases, seasonal and geographical distribution of JE cases from a tertiary care hospital in South Assam. CSF and serum samples were collected from clinically suspected AES cases and tested for IgM antibody against JE by JE MAC ELISA. Out of the total of 375 AES cases , 80 ( 21.3 %) were positive for JE. .The JE positivity was much higher(24.7%) in adult, than in paediatric population(13.4%).Significant numbers of JE cases were found to be clustered around the monsoon season. All JE positive cases had fever, whereas, 91.5% cases had change in mental status followed by headache (66.3%), neck rigidity (62.5%), unconsciousness (58.8%), seizures (27.5%) and paralysis (12.5%).