Adenophora triphylla is commonly used in food materials and oriental medicine as an analgesic, anti-inflammatory, and antitussive. In the present study, the leaves and roots of A. triphylla were extracted with water and ethanol, respectively, to examine the extracts' in vitro antioxidant activities and total phenolic contents, as well as A. triphylla's potential as a new functional food source and safe and inexpensive supply of antioxidants. Different antioxidant tests were employed and the results were compared with ascorbic acid as a standard antioxidant. The total extractable contents of phenolic compounds and flavonoids, which relate to antioxidant activity in medicinal plants, were also measured. The leaf extracts had notable levels of total phenolics and flavonoids and showed high radical and nitrite scavenging activities as well as inhibition activity against enzymes that induce oxidation. These results suggest that A. triphylla leaves are a potential ingredient for food supplements and a natural source of antioxidants.