Sad ol Din () is a village in, and the capital of, Kavir Rural District in Sheshtaraz District of Khalilabad County, Razavi Khorasan province, Iran.
At the time of the 2006 National Census, the village's population was 1,965 in 533 households. The following census in 2011 counted 1,929 people in 611 households. The 2016 census measured the population of the village as 1,931 people in 646 households, the most populous in its rural district.