Barnardo's Cymru is hoping to raise tens of thousands of pounds in September by organising the first marathon to be held in Cardiff in 10 years.
The charity hopes the event will attract more than 1,000 athletes. It is sponsored by electrical superstore Powerhouse and is organised in conjunction with Cardiff County Council, the South Wales Echo and World Masters Marketing.
"A lot of people are fed up with traditional fundraising and we're hoping to challenge people and really get them thinking about what they're raising money for,
said Jean Summerhayes, event co-ordinator at Barnardo's Cymru.