Pearline Williamson, whose grandson is 100m runner Simeon Williamson, was out shopping when a young woman ran past her, pulling the purse from her hand.
Without a thought for her own safety Mrs Williamson sprinted after the woman, believed to be in her early 20s, and managed to catch her.
The furious pensioner then shook her attacker in front of fellow shoppers in Edmonton, north London. The thief dropped the purse and escaped.
Mrs Williamson said: "She must have thought I was an easy touch because I'm elderly.
"When she took my purse I had to do something so I ran after her and grabbed her as hard as I could. She said she hadn't taken it at first, so I shook the life out of her until she finally gave it back."
Olympic hopeful Mr Williamson, 22, said: "It's typical of her as she stands up for everyone else, so it's no surprise she stood up for herself.
"She can be very friendly but also pretty scary when she wants to be – you wouldn't have wanted to be the thief.
"And there's no controlling her – you just have to stand back and hope she's alright as she doesn't think about the consequences."
Mrs Williamson said she had her purse stolen four-years ago on a bus and since then she has vowed to fight back against criminals.
She added: "I have never been scared of anyone. If I see someone being taken advantage of I do something.
"It makes me so mad when people try and take your things. Back in my day you had to work so hard for every penny. "My kids tell me not to get involved, but you have to try – if you don't do anything then bad people get away with bad things."
Her grandson will race at the Beijing Olympics as Britain's number one sprinter. He clocked a personal best of 10.03sec at the recent Olympic trials.
Mr Williamson said: "Her attitude would make her an Olympic gold medallist if she were just a few years younger.
"She's from a different generation and had to work for everything she has, so if someone takes what's hers then she will defend it. "It's that sort of stubborn belief that makes you a champion and that's exactly what she is."
