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Ten species the mosquitoes of the genus Aedes, subgenus Stegomyia were report in Taiwan. Among them Ae. aegypti and Ae. albopictus are known to be important vectors of dengue fever. The two species of Aedes were recorded from Taiwan as early as 1901. Several outbreaks of dengue fever in Taiwan wewe recorded in the 20th century. The purposes of this study are (1) to understand the seasonal abundance of Aedes populations. and (2) to understand the relationship between the distributional of vector mosquitoes and physical environment in Taiwan, especially in climatic factors. The authors come to the following conclusions: 1. Ae. aeqypti (1) The Ae. aegypti are mostly distributed in south of Taiwan, especially in Kaohsing coun-try and Liuchiu area. The high density appear during the month of May to October. (2) The temperature is the main cause of influence on Ae. aegypti distribution, Generally, the temperature range of 22℃~26℃ is most favorable, and the temperature higher than 30℃ or lower than 18℃ are unfavorable to their growth. (3) The amount of rain fall may have some influence on density of Ae. Aegypti, but is not much. The reason why is that Ae. aegypti breeds indoors. (4) Very few of Ae. aegypti are found in the areas north to Chiayi country. It remains to be clarified whether it is related to “annual variation of monthly mean temperature” or not. 2.Ae. albopictus (1)The density of Ae. albopictus in the coastal aera is lower than in the inland area. The possible explanation is that the coastal areas have stronger wind than the inland area. (2) The low density values appear in Taiwan, Penghu and Chiayi counties. It remains to be clarified whether the low density the strong northern wind or not. (3) The larvae density is higher in the northern and middle parts of Taiwan than in the southern part. It remains to be clarified whether this phenomenon is related to lower temperature in the north, or related to some other factors, such as species competion between the two. (4) The distribution of the species during the months January to May and September to December, fits very well with the isohyet maps.