Tens of thousands of people have been protesting in Kuwait City against national assembly elections due to take place on Saturday.
Opposition MPs say an amendment to voting laws manipulates the ballot in favour of pro-government candidates.
Carrying banners reading "absolute power corrupts", demonstrators called for an election boycott and for the amendment to be repealed.
Kuwait has experienced months of unrest over the rule of Sheikh Sabah al-Sabah.
The crisis was sparked in June, when the Constitutional Court annulled parliamentary elections held in February, in which the Islamist-led opposition made significant gains. The court also reinstated the previous assembly, allied to the ruling family.
After months of protests and confrontations between the opposition and the government, Kuwait's emir ordered the dissolution of that parliament and announced new elections.
Last month, he issued a decree cutting the number of candidates a voter can elect from four to one, saying it would ensure a fairer representation of people in the parliament.
'Support Kuwaiti rights'
But protesters are angry at what they see is a unilateral decision by the emir to skew the election, which will not create a parliament representing the people, says the BBC's Shaimaa Khalil in Kuwait City.
The rally was led by former Islamist MPs, by liberals and by young people, our correspondent says, adding that the mood was jubilant but defiant.
Demonstrators marched through Kuwait City chanting, "we are boycotting" and "the people want to bring down the decree".
Unlike the recent unauthorised protests, which ended in violent clashes between protesters and police, authorities issued a permit for Friday's peaceful march.
Opposition MPs say the amendment breaches the Gulf state's constitution. As a result they decided not to participate in the election.
Former MP Falah al-Sawagh told our correspondent the rally was not just about an electoral law, but about a long-term plan for real reform in Kuwait.
"This is just the beginning," he said.
Demonstrator Rana Abdel Razak said the march would continue even after the election was held.
"We want real democracy, having elections doesn't mean we have democracy," she added.
Another protester said the aim of the rally was to support the rights of the Kuwaiti people and reject any law issued outside the Kuwaiti National Assembly which was elected by the Kuwaitis.
Kuwait's parliament has the most powers of any elected body in the Gulf and opposition MPs openly criticise the ruling Sabah family.
However, the Sabahs retain full control over key government and executive posts.
The emir has dissolved parliament four times since 2006.