This paper is the first taxonomic revision of Euphorbia subgenus Chamaesyce in Iran since the publication of Flora Iranica in 1964. We provide a key, descriptions, and illustrations for the eight species of the subgenus occurring in Iran. Euphorbia nutans is reported as a new record for the flora of Iran, E. humifusa is recognized to have two forms, pilose and glabrous; the pilose form is a first report for Flora Iranica, and E. granulata var. turcomanica is reported as a synonym of E. granulata. The following information is given for each species: accepted name, synonymy, habitat, ecology, and geographical distribution.