Stretching from the Caspian Sea in the west to the western part of northeast China in the east, and central Asia is a transition belt between high latitude and low latitude areas. The and climate of this geographic region has environmental effects far beyond its borders. In this study, the dry/wet trend in and central Asia was examined over a temporal scale of 100 yr. Dry/wet change in an area is affected not only by precipitation, but also by temperature, because of its effect on potential evaporation. To more accurately describe the dry/wet trend, a drought index (DRI) was developed and calculated from gridded monthly air temperature and precipitation data from the Climate Research Unit, University of East Anglia, UK. Analysis of the DRI shows a general warm and dry trend for the region for the whole period between 1901 and 2002, A dry trend is seen in particular in the western part of Uzbekistan and Turkmenistan, central Kazakhstan, southern Xinjiang in China, and central Mongolia for the same period, while in northern Xinjiang, China, there was a weak wet trend. Over the past 100 yr, central Asia has experienced 6 wet-dry cycles: 1901-1910, 1911-1925, 1926-1935, 1936-1950, 1951-1960, and 1961-2002. The period and trend of the DRI are different from those of precipitation for the last 100 yr. The DRI can be used as an indicator of dry/wet change in and central Asia because it reflects the concurrent effects of temperature and precipitation.