Climate is the most important factor which control desertification .In order to detect climate changes in desert zones, time trend analysis is applied to extreme indices in Kashan station using extreme climate index software (ECIS). Results show significant trends in extreme indices during the past decade 1995-2004 and the pronounced warming is associated with a negative trend in cold extremes. The finding revealed that the frequency of warm (cold) extreme indices is increased (decreased) and probability, the problem of desertification in Kashan region will be extended. Keywords: Climate change; Desertification; Extreme Climate Indices; Trend, Return Period.