Organisers say more than 50,000 people are expected to take part in the annual New Year's Day protest, less than one month after an official public consultation for the city's future electoral system opened.
Beijing has pledged that the important trade hub, which was given a semi-autonomous status after it was returned by Britain to China in 1997, will be able to choose its own leader in 2017.
But critics fear democrats and those critical of Beijing will still be filtered out in the nomination process.
One of their main concerns is that Beijing will control the list of candidates who can stand for election in 2017, restricting voters' choices despite the offer of universal suffrage.
"This (protest) will be... To let our government and the CCP [Chinese Communist Party] know that Hong Kong people need and want a real democracy," Johnson Yeung, convenor of rally organiser Civil Human Rights Front, told AFP.