A cross sectional epidemiological study looking back to 158 supervised Japanese encephalitis patient in Thai Binh during the period of time from 2004 to 2010. The results showed that, the average rate of encephalitis infection in the time from 2004 to 2010 was 1.3/10 exponent 5. The rate of infectious patients per 10 exponent 5 people was highest in Dong Hung district and lowest is Vu Thu district in Thai Binh province . Encephalitis started emerging in April increasing in May to July and reaching to a peak in June in each year. The rate of infectious patients per 10 exponent 5 people was highest in group of 10 to 14 years old, gradually grows down in group of 1 to 4 years old, under 1 years old, 5 to 9 years old and group of 15 years old and up respectively. Among 158 confirmed encephalitis patients, male contributes to 55.7 percent of total and female does 44.3 percent. Conclusion: encephalitis was local circulation and there was no significant difference between urban and rural in term of prevalence. Encephalitis was naturally seasonal and usually occur in children under 15 years, there was no significant difference between male and female.