As for other towns of Iran, the name has thus been changed by the Islamic Republic authorities into Mehdishahr to punish the locals and to signal its imposed pure Muslim identity.

Since Bahais believed that the savior, Bab (Mehdi) had appeared, the Islamic Republic renamed Sangesar to Mehdishahr.

At the time of the 2006 National Census, the city's population was 20,581 in 5,473 households,[8] when it was capital of the former Mehdishahr District of Semnan County.

Sangsar, specially the northern part of it, is completely mountainous with cold winters, heavy snowfalls but with mild summers.

The most important network of roads consists of Semnan to Sangsar to Shahmirzad to Fooladmahale axis which connects these places with the city of Sari.