Two new alien plant species are reported for Bulgaria: Amaranthus viridis (Amaranthaceae) and Euphorbia serpens (Euphorbiaceae). Both are collected in Varna city, Black Sea Coast floristic region. The article provides brief morphological descriptions of the species; comments on the main distinguishing characters from the similar species; data about the localities of the species in Bulgaria and photos of the plants. The possible ways of introduction are discussed. A. viridis has been observed annually since 2013; E. serpens was discovered in 2016.