An Epidemiological Study of J.E. virus was carried out in 1982 covering two kecamatan namely Badung and Bangli, Denpasar, Bali. Badung is recognized as an endemic area of DHF and suspected J.E, whereas Bangli is endemic of DHF only. Blood samples were collected from 587 children as 1-17 years old and from 220 young pigs while light traps were used for Culex collection in the sorrounding of JE cases. The JE virus transmission rates found are as follows : In Badung and Bangli, the transmission rate among the children was respectively 30% and 2%, while among the young pigs respectively 80% and 64 %.Mixed infections with Dengue virus were found in Badung and Bangli respectively 20% and 0%. As the dominant Culex species were found C. tritaeniorhynchus and C. fuscochepala in Badung and C. tritaeniorhynchus in Bangli.