The two leading ladies played up their onscreen rivalry when they appeared before fans, with Oscar winner Theron throwing a few jabs at the Twilight star.
The South African actress admitted she had yet to spend much time with Stewart, but had a feeling she was going to "give me a run for my money".
She added, "And I'm ready for it, let's go!"
Theron went on to outline her plans for the Evil Queen's character and warned Stewart to "watch out".
She said, "It's important to me to really understand... where she came from and what drives her to get to where she is. It won't be the Evil Queen who (just) shows up evil. There's going to be a lot of circumstances that bleed into her action. I don't want to just be evil.
"And trust me, she's dark. She's a serial killer. I'm pretty much preparing to play a serial killer. I'm trying to ground it and make it something real. Watch out, Kristen."
Producer Joe Roth also touched on the rival Snow White picture currently in the works, starring Lilly Collins in the lead role, and insisted his project would challenge the traditional fairytale as a "tough, rough, active male-female picture".
He said, "Our movie is on the scale of The Lord of the Rings, in terms of size, scope and appetite. From the pictures, the other (adaptation) looks like a softer version."
Snow White and the Huntsman is due to begin production next month (Aug11) and is scheduled for release in June, 2012.