Carum copticum L. is a medicinal plant of the Apiaceae family with medicinal properties. In this study, the effects of UV-B radiation on the photosynthetic pigments and essential oils as well as phenols and anthocyanin of the seedling and callus of C. copticum were investigated under in vitro conditions. For this purpose, the experiment was set up in a completely randomized design, with three replicates per treatment. The seedlings and calli of Ajwain were categorized in two groups: the first group served as control and the second group was exposed to artificial UV-B radiation for 30 min at 15 days. The results indicated UV-B treatment reduced fresh weight about 34% and 27% compared with control in seedlings and calli respectively. The amount of chlorophyll a, b and total chlorophyll as well as carotenoids decreased about 36%, 42%, 38% and 14% in seedling and 24%,32%, 26% and 14% in callus of C. copticum respectively under UV stress. The lowest and highest amounts of flavonoids and anthocyanin were observed at UV-B treatment and untreated plants respectively. In addition, The UV-B stress changed the compounds of the essential oil both in the seedlings and the calli of C. copticum. Analysis of the essential oil constituents showed thymol and gamatherpinen, the main essential oil components of C. copticum, increased under UV-B radiation. While, p-cymene concentration decreased under UV treatment Therefore, C. copticum is useful for the in vitro production of pharmaceuticals and other beneficial substances by plant tissue culture techniques under UV-B treatment. Manuscript profile