Police fired tear gas, rubber bullets, stun grenades to break up the demonstration, Iran's Press TV reported.
More than 100 protesters were injured, the Iranian broadcaster said. Medical sources said dozens of people showed up at hospitals suffering from tear gas inhalation and baton bruises.
"The number of wounded protesters in hospital has exceeded 100 after riot police attacked them," Mohammad al-Humaidi, director of the Kuwait Society for Human Rights, said.
The Kuwaiti news agency KUNA reported the Interior Ministry said 11 security personnel were injured and government vehicles were damaged by stones thrown by the demonstrators.
Former Member of Parliament Abdullah al-Barghash and other activists said more than 100,000 people took part in the protest, Press TV said.
The protesters contend the government's changes to the country's election laws amount to a constitutional coup, Press TV said. The government said last week it would hold elections Dec. 1, a move the activists say is meant to result in the election of a Parliament compliant to the wishes of Emir Sheik Sabah al-Ahmad al-Sabah.
Kuwait has had an elected Parliament in 1962, thought the al-Sabah family retains control of most key posts, Press TV said.