Recently, studying essential oils and secondary metabolites of plants and microalgae have received much attention. The biosynthesis of the secondary metabolites is strongly influenced by different environmental factors. Monoterpenes as a main fraction of essential oils of fruits and vegetables have many clinical applications. They could inhibit the carcinogenesis processes and therefore might be effective in treatment of cancers. Dunaliella salina, a photosynthetic green microalga is known as a rich source for β-carotene production. In this study, the effects of some monoterpenes including menthone and piperitone was investigated on yield of production of β-carotene were studied. Menthone and piperitone as parameters of stress can make tensions to the medium of D. salina increasing its β-carotene and chlorophyll a content in every single cell but on the other hand these two monoterpenes cause a decrease in the concentration of β-carotene and chlorophyll a. © 2016 Mina Zarei et al.