The singer, 53, told the Sunday Mail newspaper that she had "so much love to give" and it would make her "so happy."
"I have so much love to give. I want to adopt a child who doesn't have much, who I can really give something to. We'll have to see what social services say, but it would make me so happy," she said.
Susan, who finished second on reality TV show Britain's Got Talent in 2009, had been considering the move since last year and has already started the adoption process.
"I know I'm single and 50-odd. People don't think I'm serious when I say it, they have a giggle at me. Let's see."
Just last year, Susan, who is worth more than £22million, revealed exclusively to HELLO! magazine that she suffers from Asperger syndrome, a form of autism that affects communication and social interaction.
"It's hard but having Asperger's doesn't mean I can't get on with a normal life," she said. "However, it is tougher in the music industry - they don't understand it."
"Any change in life, so quickly, is stressful because one minute you're at home with your cat and the next you're away with all of the camera people. Now I'm getting used to it; I have to get used to touring."