Abstract. Kuntorini EM, Dewi M, Misrina. 2016. Anatomical structure and antioxidant activity of red bulb plant (Eleutherine americana) on different plant age. Biodiversitas 17: 229-233. Eleutherine americana Merr is an medicinal herb named “red bulb” or “bawang dayak”. Red bulb plant is commonly used as anti-breast cancer in Kalimantan, which may be linked to their bioactive naphtoquinone-derivatives properties. The aim of this study was to characterize the anatomical structure and antioxidant activity in red bulb of different ages. The anatomical structure of bulb was fixed and prepared following paraffin embedding techniques. Measurement of antioxidant activity carried out using the DDPH method. The anatomical structure of red bulb showed that the P2 (12 week after planting (WAP)) bulb is thicker in the upper and lower epidermis, parenchymal, and vascular bundles than P1 (6 WAP) bulb. The result of antioxidant activity of P2 (12 WAP) with IC50 = 50.42 ppm have stronger antioxidant activity than the P1 (6 WAP) with IC50 = 93 ppm, but weaker than vitamin C (IC50 = 3.03 ppm) and BHT (IC50 = 5.52 ppm) as a control. Keywords: Anatomical structure, antioxidant activity, Eleutherine americana, red bulb