Purpose: To evaluate the antioxidant, anti-inflammatory, inhibitory and cell proliferation activities of Cirsium japonicum (C. japonicum) var. spinossimum.
 Methods: Phytochemicals (polyphenols, flavonoids, and silymarin) in leaves, roots, and seeds of C. japonicum var. spinossimum were quantified using high-performance liquid chromatography (HPLC). Antioxidant activity was investigated on 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. Anti-inflammatory activity was investigated on nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW264.7 cells. Immunostimulant and hair loss prevention was confirmed through 3'-{1-((phenylamino)-carbonyl)-3, 4-tetrazolium}bis(4-methoxy-6-nitro)benzenesulfonic acid hydrate (XTT)-based cell proliferation assays using Jurkat cells and human follicle dermal papilla cells (HFDPC).
 Results: Extract from seeds exhibited the highest total polyphenol content (610.08 ± 32.40 mg GAE/g), as well as the highest total flavonoid content, while the total polyphenol content of leaves and root extracts were similar. The RC50 values for seed extract against ABTS and DPPH radicals were 8.20 ± 0.02 µg/mL and 40.13 ± 2.47 µg/mL, respectively. In particular, all six Silymarin derivatives were found to be highest in the seed extract. The C. japonicum var. spinossimum seed extract (CSE) showed significant (p < 0.05) nitric oxide (NO) inhibitory activity in RAW264.7 cells induced by LPS at all concentrations (12.5, 25, 50, 100 and 200 µg/mL) and exhibited significant (p < 0.05) cell proliferation activity in Jurkat and hair follicle dermal papilla cells (HFDPC) at 25 µg/mL.
 Conclusion: Extract of C. japonicum var. spinossimum seeds contain polyphenols and flavonoids and show significant NO inhibitory and cell proliferation activity in Jurkat and HFDPC. Therefore, Cirsium japonicum is a promising source of anti-inflammatory and anticancer agents.