The actress became the youngest celebrity to strip off for the animal rights organisation's I'd Rather Go Naked Than Wear Fur campaign at the age of 19 in 2009, and now she has shown her support for the cause again.
In a new advertisement urging her fans to quit eating meat, Serratos is shown standing in a fog-filled cemetery while sporting a corset, high heels, and ghoulish make-up, alongside the message, "Your body shouldn't be a graveyard. Factory farms are hell for animals, and their death is slow and painful. Help animals by not eating them. Respect Life. Go Vegetarian."
The actress says, "When I stopped eating meat, I noticed that it was easier for me to focus, and I was really proud of myself for being green also... I had a plethora of reasons for going vegetarian.
"I was eating meat and didn't know how it affected my health... I just felt better and brighter and lighter, and I had more energy... It was a big deal to me, being an animal lover, that I realised what I was eating, and I didn't separate myself from, say, my animals, my pets."
Stewart, who has been dating Twilight hunk Robert Pattinson for three years, stunned Hollywood last week (ends27Jul12) when she confessed to a "momentary indiscretion" with her Snow White and the Huntsman director Rupert Sanders and apologised to devotees for the controversy.
Heartbroken Pattinson has since reportedly moved out of the Los Angeles home the couple shared, but the Brit will have to reunite with Stewart in a matter of weeks as they begin to promote the November (12) release of The Twilight Saga: Breaking Dawn - Part 2.
But co-star Serratos is confident ticket sales will not be affected by the couple's fall-out as fans are still invested in the characters they play onscreen.
She tells UsMagazine.com, "Of course people are fans of us now, but I think above anything, they're fans of these characters. I don't think anyone's really gonna give a s**t. They're gonna see the movie; it's going to be awesome."
The pretty 19 year old, who plays Angela in the film franchise, brings new blood to the animal rights campaign.
The vegetarian star says, "I've always been opposed to slaughtering, eating and wearing carcasses."
Serratos joins a growing list of celebrities who have starred in PETA's anti-fur ad campaigns - they include Charlize Theron, Eva Mendes and Roselyn Sanchez.