The charity that Sam Harper Brighouse was fundraising for has pledged to use the money from his JustGiving page for a special project in his memory.
In a statement, they said:
Hundreds of people have made donations to the fundraising page of a young Londoner who died after collapsing during a marathon.
Sam Harper Brighouse is believed to have suffered a cardiac arrest at about the 16-mile mark of the Brighton Marathon yesterday.
Donations have since been flooding in to his justgiving.com page - with the total now well above £5,000. He'd originally aimed to raise just £500.
His site states that he had embarked on the challenge to raise money for the Arms Around The Child charity which supports Aids orphans.
He wrote: "I'm running, jogging, crawling the brighton marathon for Arms Around The Child (UK) (formerly KCA UK) because I am want to raise money for a good cause."
A man who died while running the Brighton Marathon has been named locally as Sam Harper Brighouse.
Twenty-three-year-old Mr Harper Brighouse was from London
A spokesman for the Royal Sussex County Hospital said the man died at 2.30pm.
England cricketer Matt Prior had officially started today's race, the fourth Brighton marathon, in Preston Park at 9am.
Organisers said 9,315 competitors were taking part.