The 3-day youth event was aimed at putting pressure on COP26 delegates as they met to plan the upcoming UN Climate Change Conference.
Ahead of the COP26 UN summit on climate change, young people met in Milan to pressure world leaders before they meet at the end of this month.
Thousands took to the streets of the Italian city on Saturday to push policy-makers to take action.
It came on the final day of a preparatory meeting for delegates from around the world to identify where progress can be made before the summit starts in Glasgow on October 31.
Activists voiced their frustration at politicians and big companies during the march, saying not enough action has been taken, despite international meetings like the COP.
"Despite the many demonstrations and the many international meetings like the pre-COP or the COP there hasn't been any turn in the politics to tackle climate change, they still talk about reaching zero emission by 2050 while we say it must be done by 2030," said 25-year-old activist Lorenzo Morandi.
The UK's president for COP26 said the presence of youth delegates and activists had energised the process.
"What we were hearing shamed this set of world leaders and there is no doubt that this group of young people and in fact young people around the world are going to hold this set of world leaders to account if at COP26, we are not able to credibly say that we have kept 1.5 degrees within reach," Alok Sharma said.
The previous day, Fridays for Future activists including Greta Thunberg and Vanessa Nakate, led another climate march in Milan.
In a speech to demonstrators, Thunberg told the crowds that politicians are only "pretending that they have solutions to the climate crisis", adding that it's only "when people gather to make change" that there is hope for the future.
The 12-day COP26 summit in early November will aim to secure more ambitious commitments to limit global warming. The meeting also is focused on mobilising financing and protecting vulnerable communities and natural habitats.
US climate envoy John Kerry who attended the preparatory conference in Milan on Saturday, said he thinks "enormous progress" can be made at the upcoming UN climate talks in Scotland but more governments must come up with concrete commitments in the next 30 days.