Both were youth-driven popular movements demanding change, led by loose coalitions of disparate factions that lacked strong leadership. And in both cases, the protesters' demands grew as the regimes clamped down.
But there are important differences between the two that may result in different outcomes. In Iran, the catalyst was the charge that the authorities had stolen an election that the opposition believes Mousavi won; the Chinese protestors had no history of voting in competitive elections and were mobilized by the death of Hu Yaobang, a reformist member of the communist leadership. China used maximum force relatively early; it contained the challenge within seven weeks. Iran's regime is losing momentum after seven months; demonstrations late last month spread to at least 10 major cities. China banned the foreign press and tightly controlled state media; Iran has been unable to prevent eyewitness accounts of citizen journalists from reaching the Internet, Facebook and Twitter.
The biggest difference may be that Iran is historically more democratic than China, where public participation in politics has been restricted for centuries. Iranians have had a growing role in politics since the 1905-11 Constitutional Revolution produced Asia's first parliament; they've voted for decades under both a monarchy and a theocracy. Also, China has long been a closed society; Iran's Indo-European population has long had exposure to Western ideas and education.
Rather than Tiananmen, Iran's opposition is hoping to repeat a different event from 1989 — the fall of the Berlin Wall and the collapse of Eastern Europe's communist regimes.
Here's hoping for a peaceful day. Take action in support of human rights in Iran here.