Anthropogenic 129I has been released to the environment in different ways and chemical species by human nuclear activities since the 1940s. These sources provide ideal tools to trace the dispersion of volatile pollutants in the atmosphere. Snow and seawater samples collected in Bellingshausen, Amundsen, and Ross Seas in Antarctica in 2011 were analyzed for 129I and 127I, including organic forms; it was observed that 129I/127I atomic ratios in the Antarctic surface seawater ((6.1−13) × 10−12) are about 2 orders of magnitude lower than those in the Antarctic snow ((6.8−9.5) × 10−10), but 4−6 times higher than the prenuclear level (1.5 × 10−12), indicating a predominantly anthropogenic source of 129I in the Antarctic environment. The 129I level in snow in Antarctica is 2−4 orders of magnitude lower than that in the Northern Hemisphere, but is not significantly higher than that observed in other sites in the Southern Hemisphere. This feature indicates that 129I in Antarctic snow mainly originates from atmospheric nuclear weapons testing from 1945 to 1980; resuspension and re-emission of the fallout 129I in the Southern Hemisphere maintains the 129I level in the Antarctic atmosphere. 129I directly released to the atmosphere and re-emitted marine discharged 129I from reprocessing plants in Europe might not significantly disperse to Antarctica.