Holding banners saying "The children of Aleppo are calling you!", or "Aleppo is bleeding and the world is watching", around 900 people braved plunging temperatures to gather in front of the Reichstag, the German parliament building, according to police estimates.
At the same time, another 1,800 people joined a second demonstration elsewhere in the German capital, police said.
"What is happening there amounts to what is the worst in the world," said Mahmoud Almizeh, a 19-year-old Syrian refugee who comes from Raqa, now the bastion of the Islamic State jihadist group.
Germany has opened its doors to some 600,000 Syrian refugees since the conflict began in 2011.
Having arrived in Germany a year ago, Almizeh lamented that European leaders were "unfortunately doing nothing".
In Aleppo on Saturday trapped Syrian civilians and rebels waited desperately for evacuations to resume from an opposition-held enclave of the city which has fallen to the brutal onslaught by Syrian government forces.
Aleppo has been ravaged by some of the worst violence of the nearly six-year war that has killed more than 310,000 people.
"We feel so powerless" about the tragedy facing the Syrians, said Anna Bone, a Berlin resident at the demonstration where another banner declared:
"Stop murdering! Peace talks NOW."
"This powerlessness... this grief, it's what brought me here today," she added.
Hundreds of protestors also joined demonstrations in France on Saturday in the cities of Paris, Lille, Strasbourg and Marseille.
"It's crazy that the world powers cannot intervene," commented two protestors of Turkish origin, Hilal, 25, and Gulsan, 26, in Paris.
Thousands of trapped civilians and the last remaining opposition fighters in Aleppo were waiting for evacuations to resume on Saturday, a day after the operation was suspended by the Syrian government.
Meanwhile in New York, the UN Security Council could vote as early as this weekend on a French-drafted proposal to allow international observers into Aleppo and ensure urgent aid deliveries.