Poshtkuh-e Mugui Rural District () is in Mugui District of Fereydunshahr County, Isfahan province, Iran. Its capital is the village of Masir.
At the National Census of 2006, its population (as a part of the Central District) was 4,747 in 897 households. There were 4,359 inhabitants in 1,036 households at the following census of 2011. At the most recent census of 2016, the population of the rural district was 3,711 in 948 households. The largest of its 51 villages was Koluseh, with 691 people.
After the 2016 census, Pishkuh-e Mugui and Poshtkuh-e Mugui Rural Districts were separated from the Central District in the establishment of the new Mugui District.