The 29-year-old singer, who has beaten Britney Spears (35 million), Rihanna (34 million) and Justin Timberlake (30million), expressed her happiness to become the most popular celebrity on the micro-blogging site.
"Oh yeah and we grew to 50 million Katycats! Eh, regular day at the office," she posted.
After Perry, second in line is Justin Bieber with 49,200,172 followers, while Lady Gaga, who made Twitter history when she became the first person to claim 20 million followers, is now in fourth place with 41,026,779 followers.