Phenylpropanoids are a large and important family of plant secondary metabolites. The biosynthetic pathway of phenylpropanoids is induced in plants under environmental stresses to cope with these harmful conditions. In the present study, for the rst time, we identi ed and characterized one reference gene (ACTIN) and three key biosynthetic genes (4CL, C4H and CVOMT) in the Iranian red and green cultivars of sweet basil. Also, the expression patterns of 4CL, C4H and CVOMT biosynthetic genes were determined for the rst time in the Iranian red and green cultivars of sweet basil under cold, drought, heat, light and salt stresses. The results showed that the ACTIN, 4CL, C4H and CVOMT genes identi ed in the Iranian cultivars are identical to other cultivars in terms of all characteristics such as ORF length, protein sequence length, molecular weight, functional domains, lack of signal peptide, subcellular localization site, and secondary structures. Our results also revealed that the 4CL, C4H and CVOMT biosynthetic genes have different expression in the Iranian red and green cultivars of sweet basil under abiotic stresses and their expression patterns are cultivar-dependent. The ndings of this study can advance our knowledge of phenylpropanoids biosynthesis in plants under environmental stresses. These ndings also can be used in plant breeding programs for stress tolerance in sweet basil and other plants.