Abstract: Abstract:Using both qualitative and quantitative methods this paper investigates the similarities and differences of the Aral Sea and Lake Balkhash through analyzing the hydrological characteristics,runoff features of the main inflow rivers,human activities in the catchments,related eco-environmental issues and the future trends.The results show that,the water level in the Aral Sea decreased sharply since 1960,until a nearly single trend of water level variations.The entire water body of Aral Sea was splitted into four areas by 2009.On the other hand,the water level fluctuations in the Lake Balkhash followed a cyclical pattern over the long term,especially,the water level had been dropping since 1970 and reached a minimum value in 1987.The study reveals an unsatisfactory situation in the hydrological regime of Aral Sea,as the entire water body may eventually dry up in the near future.The water level condition cannot be ignored in Lake Balkhash,as it is currently undergoing a change from water surplus surplus to shortage.The study recommends that all the riparian countries including the Aral Sea and Lake Balkhash should have an important responsibility in the protection of transboundary water resources and eco-environment conditions.