Dengue fever (DF) is a mosquito transmitted viral infection disease. Vietnam is one of the eight countries in the world have highest morbidity and mortality of DF. The disease occurs all over the country. This study was conducted in Cat Sa in 2013 with the objectives to study the epidemiology characteristics of DF and identify the hot spots of DF here. The results show that DF occured in women was more likely than in men. Age group 40 - 44 years old was the highest and the most risky group. Similarly, Fishermen and household workers had the higher risk than people working in other jobs. During 2013, the case numbers were the highest in September and October. Moreover, people who living near dengue cases within 70m and 5 days was 3 to 20 times more likely to be infected with DF. There are two hot spots have been detected in'the centre of Cat Ba town and sea off of Cat Ba island.