The actress made her last appearance on The CW drama in the third season's penultimate episode 'The Prom Before the Storm'.
However, she will reprise her role as Debbie Wilson in the fifth season premiere - due to air on October 8 - according to TVLine.
47-year-old Loughlin originally exited 90210 last year, suggesting that her character was not being given "enough to do".
"It is a very big cast and it is hard to service all of us," she said in February 2011. "The focus of the show is the kids [and] the parents were essentially there to service the storylines of the kids.
"Occasionally we got a few separate storylines, but it just wasn't really working in a way that all of us had enough to do."
90210 airs on The CW in the US and on E4 in the UK.
> 90210 star Trevor Donovan returning for season five
> 90210: Justin Deeley to depart in season five
Watch a clip from 90210's fourth season finale below: