Five new alkaloids (1-5), including three new aporphine alkaloids and two new phenanthrene alkaloids, together with 10 known compounds (6-15) were obtained from the roots of Stephania tetrandra. Their structures were elucidated by spectroscopic methods, single-crystal X-ray diffraction, and electronic circular dichroism analyses. Compounds 7-10, and 13 showed antioxidant activities with malondialdehyde (MDA) inhibitory rates of 62.50 ± 1.91 to 98.44 ± 0.34% at the concentration of 10 μM.