Andrographis paniculata has a long history of use in traditional medicine and andrographolide is one of its potent compounds. In this study, a rapid isolation of andrographolide (colourless, bitter and crystalline diterpene lactone) was carried out by a newly developed microwave-assisted extraction. The extraction intensity, time and amount of solvent were optimised prior to this. The conventional heating method provided a 0.4452% yield of andrographolide and microwave heating at 210 W for 40 min provided a 0.589% yield. Compared to conventional extraction procedures, the results suggested that the proposed method was an effective alternative for the extraction of andrographolide. The isolated compounds were found to be the same by UV, HPTLC and 1H-NMR studies. The isolated andrographolide was tested for in vitro antioxidant activity, and showed a potent free radical scavenging activity.