Masabi Rural District (Persian: دهستان مصعبي) is in Ayask District of Sarayan County, South Khorasan province, Iran. Its capital is the village of Masabi.

At the National Census of 2006, its population was 2,445 in 852 households. There were 1,865 inhabitants in 749 households at the following census of 2011. At the most recent census of 2016, the population of the rural district was 1,682 in 706 households. The most populous of its 30 villages was Karimu, with 679 people.