||Aridity is a permanent feature of climate based on long‐term climatic conditions over a region. Climatic indices are reliable tools to explore climate type, and climatologists have proposed various indices to classify climate and investigate the aridity or humidity in any region. In this study, we examined spatiotemporal variations of aridity in Iran during the last six decades from 1954 to 2013, using the de Martonne aridity index (IDM), which is calculated based on precipitation and temperature. Data used in this study were extracted from the Global Precipitation Climatology Centre and the University of Delaware gridded data sets, respectively. Both data sets have global high‐resolution (0.5° × 0.5°) coverage, and temporally span more than a century of data (from 1901). According to the data obtained from these data sets, more than 80% of Iran has an arid and semi‐arid climate (annually), although the spatial pattern of IDM varies throughout the year. Using the Mann–Kendall test showed a negative significant trend in IDM in 20% of Iran's total area in spring, and less than 7% in the other seasons of the year. Overall, it can be concluded that there were no significant trends in aridity for most parts of Iran during the last six decades.