Sim () is a town in Ashinsky District of Chelyabinsk Oblast, Russia. It is located on the Sim River, west of Chelyabinsk and is the administrative center of the oblast. Population:
It was founded in 1759 and named Simsky Zavod (, lit. Sim's Plant). The settlement was formed around an ironworks. It was renamed Sim and granted town status on November 13, 1942.
Within the framework of administrative divisions, it is incorporated within Ashinsky District, together with two rural localities, as the Town of Sim. As a municipal division, the Town of Sim is incorporated within Ashinsky Municipal District as Simskoye Urban Settlement.
It is the birthplace of Igor Kurchatov, a famous Soviet/Russian physicist.