The 2008 gold medallist recorded the video during a training break at the Olympic Village in London and uploaded the clip to his YouTube account.
Mitcham said: "Someone on twitter asked me to upload a video of me playing the ukulele. I profess to be neither a great instrumentalist nor singer.
"I'm just an Olympic diver who likes to strum away in his spare time."
The Australian will compete in the men's 10m platform diving event on Friday, August 10.
He is the defending champion after performing the highest-scoring single dive in Olympic history at the Beijing Olympics back in 2008.
Photo gallery - London 2012 Olympics:
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