Danish astronaut Andreas Mogensen, accompanied by Russian cosmonaut Sergei Volkov and Aidyn Aimbetov from Kazakhstan, had taken 26 custom-made figurines from Danish toymaker Lego on the ride to the station.
The trio blasted off aboard a Soyuz rocket from the Baikonur cosmodrome on Wednesday but the trip lasted two days instead of the usual fast-track six hours after the ISS raised its orbit to avoid space debris.
They joined six astronauts already in space, bringing the total number of people on the ISS to nine, for the first time since 2013, according to the European Space Agency.
Accompanied by veteran Russian cosmonaut Gennady Padalka, first-time flyers Aimbetov and Mogensen will return to Earth next week after 10 days on the station.
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Aimbetov, who replaced British singer Sarah Brightman after she pulled out of the mission in June, is the third astronaut from Kazakhstan, which hosts Russia's cosmodrome.
The trio led by Padalka, who has been in orbit since June, are set to leave the orbiting space station on September 12.
Russia is the only country still sending its own craft to the ISS after NASA ended its space shuttle programme in 2011 and turned to private firms to fly supply missions there.