This research was carried out to determine whether the changes in precipitation and temperature trend in Iran are attributed to climate change or natural climate variability. The trend and its magnitude with the climatic extremes indices considered by Expert Team on Climate Change Detection and Indices were analysed based on the quality-controlled daily data of 37 meteorological stations by nonparametric Mann-Kendall test and Sen's slope method from 1966 to 2015. Results indicated that TXx, TNn, the average maximum, and minimum temperature indices have increased with a significant trend in most parts of Iran. The minimum temperatures (TNn and annual Tmin) were increased more rapidly than maximum temperatures (TXx and annual Tmax) and rising temperatures have occurred in northern latitude and western regions more than elsewhere. As a result, the temperature increase leads to changes in seasons and season length; and reduces the growing season of a