The 24-year-old gave a touching speech during a celebrity fundraising dinner in New York as he carried out his first official overseas duties.
The royal pledged to take forward his mother's crusade to help affected African children or those orphaned by the fatal disease.
Harry further explained how he came up with his charity Sentebale in Lesotho with a prince, who like him lost his mother at a young age.
"Prince Seeiso and I both lost our mothers when we were young. We set up Sentebale in their memory. Sentebale is the Lesotho word for the flower forget-me-not," the News of the World quoted him as saying.
"This beautiful kingdom has been ravaged by HIV/AIDS and poverty, leaving thousands of children without parents to look after them.
"We hoped to create a charity that would transform children's lives, giving them a sense of hope and security. We really do believe that Sentebale is doing this," he added.
Harry is due to return to the UK on May 31 to resume his training to become a combat helicopter pilot.