Transmission of Dengue Hemorrhagic fever by Aedes aegypti mosquito is influenced by several environmental factors, namely temperature, humidity, and rainfall. This study aims at identifying the relationship between environmental factors and dengue vector population density. A longitudinal entomological study was performed in the city of Kassala, Sudan, in 20 households in each of the 20 clusters during the three seasons of 2014 and 2015. Data were collected using spotlight in any water-holding container where immature stages of Aedes spp. were detected. Immature mosquitoes were counted and classified into larvae and pupae. Ambient temperature and relative humidity in each cluster were recorded, and the total rainfall of Kassala City was obtained from the main Meteorological Station in Khartoum. There was a significant positive correlation between rainfall and number of Ae. aegypti females at Garb Algash and Khatmia areas. Larval instar 4 and pupae were positively correlated with high humidity at Khatmia and Altora areas. In autumn season, there was no strong correlation of all the stages with all climatic variables. There was also positive significant correlation between ambient low temperature and number of females in autumn season.