Robert Sherwood, the 9-year-old begged his parents to let him take a blood test to see if he could help his brother 5-year-old Edward, who was suffering from the disease which causes his bone marrow not to produce enough new blood cells.
The condition, which affects just two children in Britain every year, leaves sufferers at high risk from infections.
Edward needs to take drugs every day, and doctors warned his parents Susan and Kelly that he (Edward) probably would not live to see his 10th birthday unless a suitable donor could be found.
Luckily, the test was a success, and doctors confirmed Robert was a perfect match.
"I'm looking forward to helping my brother and I don't feel too scared. This is my special Christmas present for him," the Daily Express quoted Robert as saying.
"I want Edward to get better so we can play together without him getting hurt," he said. Housewife Susan, from Didcot, Oxon, and Kelly, a recruitment consultant, are preparing for the operation at the Bristol Royal Hospital for Children on Jan 7. "Everybody is so proud that Robert stood up and offered to have the operation. He's a true hero," Susan added.