In this study, total seasonal and annual rainfall data in a 50 years period (1961-2004) of 12 synoptic stations of Iran were obtained from Iran Meteorological Organization (IRIMO). All time series have been checked for normality with the Kolmogorov-Smirnov test. The seasonal and annual trends of rainfall were analyzed using nonparametric technique of Mann-Kendall's for level of significance of 95 and 99 % (sig.95, 99%). The results showed that out of total 60 annual and seasonal time series, 13 series have significant trend (sig. 95%) from which two series had significant trend in sig.99% also. The significant trends of different stations were both increasing and decreasing. In none of the individual stations, annual and seasonal series showed both positive and negative trend, in other words, all trends were either negative or positive. The most significant trends were observed in winter and annual series, such that among the 12 study stations, four stations in winter season series and four stations in annual series had significant positive or negative trend (sig.95%). In case of spring time series, three stations had negative significant trends at sig.95%. In both summer and autumn time series, only one station showed a positive trend at sig.95%. Among theses stations, four ones did not show any significant trend in seasonal and annual time series.
