The 'Last Friday Night' hitmaker - who is married to British actor-and-comedian Russell Brand - shunned a big bash in favour of hosting a discreet party for 60 friends at the Electric Cinema in Birmingham, West Midlands, where guests were treated to a showing of The Cult classic.
Katy - whose birthday coincided with a night off from the UK leg of her 'California Dreams' world tour - said: "It was my first time."
She later tweeted: "My friends are the best present a girl could ever dream of."
To mark her birthday last Monday (25.10.11), Katy also took to her twitter page to ask fans to make a donation to her favourite charity.
She wrote: "Thanks for the sweet B-day messages! For my b-day I have set up a donation page @aspca.org/katyperry The voice for ANIMALS! Give if u can!
" ooo... it's trending. i feel shpeshul. (sic)"
During her time touring the UK, the singer has been treating herself to a number of traditional British dishes, including dining on meat pies and Yorkshire puddings when she arrived in Sheffield, North England, where she started her run of shows.
However, after gorging on baked beans - a canned snack in tomato sauce - Katy has been suffering from flatulence, the food's major after-effect.
She recently said: "I love coming to London so I can have baked beans on toast. They do bloat me and I'm afraid I'm going to go off like a firework, but I do love them."