Activists and citizens rallied at the US capital's National Mall and are now marching to the Lincoln Memorial and a new monument, the Martin Luther King Jr. Memorial.
They came together just four days before King made his historic speech 50 years before, raising concerns about jobs, voting rights and gun violence.
On Wednesday, the actual anniversary of the speech and the March on Washington, President Barack Obama will speak at the Lincoln Memorial.
Former presidents Bill Clinton and Jimmy Carter are expected to join Obama for the event.
Among those expected to speak at the event is the mother of Trayvon Martin, the black teenager shot dead in Florida last year by George Zimmerman, who was recently acquitted.
Other issues being discussed at Saturday's rally included income inequality, discrimination based on sexual orientation and mistreatment of immigrants.
"I am a daughter of the civil rights movement, and as a daughter I am a beneficiary of all the good that resulted from the hard work, the sweat and tears, and the blood that was shed by the leaders and doers of that movement," Jennifer Jones Austin of the Federation of Protestant Welfare Agencies told the crowd. "And as a daughter and a beneficiary, I am now the burden-bearer of this generation's civil rights movement."
Rev. Al Sharpton and King's son, Martin Luther King III, led the event.
King, who was assassinated in 1968, led about 250,000 people in 1963 to the same place where Saturday's rally took place and delivered his historic speech where today's activists now stand.
He said: "I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character."