Both men were treated by paramedics after completing the 13.1-mile race, ambulance officials confirmed.
They were among the 25,000 runners to take part in the 15th anniversary of the race.
One of them was believed to be in his 20s and the other one in his 30s, BBC reported.
The event organised by Run4Wales began at Cardiff Castle at 10am and finished outside the Civic Centre.
Participants ran past the Millennium Centre, Cardiff Bay Barrage and Roath Park.
Australian Jack Rayner finished first in a time of one hour, one minute and one second.
Uganda's Juliet Checkwel won the women's race in one hour, nine minutes and 45 seconds.
Officials said the race was the biggest yet and could be worth £2.3million to the economy.
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