Using indirect ELISA IgM technique detected IgM anti Banna virus from 717 cerebrospinal fluid samples of patients who has acute encephalitis syndrom unknown causes were collected from 9 provinces/cities in the North, Central, South and Highland Central from 2002 to 2012. Positive results identified the Banna virus antigen average is 184/717 (25.66 percent). On these results, sero-epidemiological characteristics of acute encephalitis syndrome virus Banna is determined as follows: (1) Propotion positive was ranged from 13.63 percent - 35.83 percent of the 9 provinces/cities, where samples were collected for the detection of IgM against Banna virus
(2) The positive cases were recorded all year round, but mainly in summer months May, June and July with highest prositive cases in June to be 34.78 percent
(3) The distribution positive cases by age groups were different age group, the lowest in age group I year old was 5.98 percent, the highest in age group or = 15 year olds was 28.26 percent, other age groups ranged 19.02 percent - 23.91 percent.