The popstar - who has turned 29 today - dug out the old childhood snap and shared it with her 45 million Twitter followers yesterday (24 October), as part of the site's weekly 'Throwback Thursday' trend.
A young Katy looked ever so cute in a navy blue sailor dress. Sitting on a bench, the star crossed her hands on her lap.
Her sailor dress was complete with a white collar adorned with a large red bow, while the stripe cuffs were complemented with big red buttons.
Katy, who sported short, light brown hair and cute little dimples, was all smiles as she posed with a perfect posture. Captioning the snap, she said: "#Throwbackthursday in my sailor moon dress!"
Although Katy now sports sleek, long black hair, we can definitely see the resemblance in the smile!
We're sure for Katy though, it's hard to believe just how far she has come. Since rising to fame in 2008, she's managed to notch up eight number one singles in the US Billboard charts.
In fact, this year alone has been pretty jam-packed for the 'Roar' singer, who released her fourth studio album Prism this week, which is set to be another chart-topping hit.
Happy Birthday Katy!
Could you recognise Katy in this childhood photo? Has she changed much since her younger days? Tell us below, as the best comment from across the website each week wins £50!
Watch Katy's music video for 'Roar' below:
Check out more celebrity childhood photos in our gallery!