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Ultraviolet B (UV-B) light, as a physical elicitor, can promote the secondary metabolites biosynthesis in plants. We investigated effects of different energy levels of UV-B radiation on growth and bioactive compounds of <i>Crepidiastrum denticulatum</i>. Three-week-old seedlings were grown in a plant factory for 5 weeks. Plants were subjected to different levels of UV-B (0, 0.1, 0.25, 0.5, 1.0, and 1.25 W m⁻²), 6 h a day for 6 days. All UV-B treatments had no negative effect on the shoot dry weight; however, relatively high energy treatments (1.0 and 1.25 W m⁻²) inhibited the shoot fresh weight. UV-B light of 0.1, 0.25, and 0.5 W m⁻² did not affect total chlorophyll and H₂O₂ contents; however, they increased total carotenoid content. On 4 days, 0.25 W m⁻² treatment increased antioxidant capacity, total hydroxycinnamic acids (HCAs) content, and several sesquiterpenes. Treatments with 1.0 and 1.25 W m⁻² increased total carotenoid, total HCAs, and H₂O₂ contents, and destroyed chlorophyll pigments, reducing maximum quantum yield of photosystem II and causing visible damage to leaves. Partial least squares discrimination analysis (PLS-DA) showed that secondary metabolites were distinguishably changed according to energy levels of UV-B. The potential of 0.25 W m⁻² UV-B for the efficient production of bioactive compounds without growth inhibition in <i>C. denticulatum</i> was identified.