Casting:
Aronofsky first discussed with Portman the possibility of a ballet film in 2000, and he found she was interested in playing a ballet dancer.Portman explained being part of Black Swan, "I'm trying to find roles that demand more adulthood from me because you can get stuck in a very awful cute cycle asa woman in film, especially being such a small person.Portman suggested to Aronofsky that her good friend Mila Kunis would be perfect for the role. Kunis contrasted Lily with Nina, "My character is very loose... She's not as technically good as Natalie's character, but she has more passion, naturally. That's what [Nina] lacks. The female characters are directed in the Swan Lake production by Thomas Leroy, played by Cassel. He compared his character to George Balanchine, who co-founded New York City Ballet and was "a control freak, a true artist using sexuality to direct his dancers".
Portman and Kunis started training six months before the start of filming in order to attain a body type and muscle tone more similar to those of professional dancers.Portman worked out for five hours a day, doing ballet, cross-training, and swimming. A few months closer to filming, she began choreography training.Kunis engaged in cardio and Pilates, "training seven days a week, five hours, for five, six months total, and ... was put on a very strict diet of 1,200 calories a day." She lost 20 pounds from her normal weight of about 117 pounds, and reported that Portman "became smaller than I did." Kunis said, "I did ballet as a kid like every other kid does ballet. You wear a tutu and you stand on stage and you look cute and twirl. But this is very different because you can't fake it. You can't just stay in there and like pretend you know what you're doing. Your whole body has to be structured differently." Georgina Parkinson, a ballet mistress from the American Ballet Theatre, coached the actors in ballet.American Ballet Theatre soloists Sarah Lane and Maria Riccetto served as "dance doubles" for Portman and Kunis respectively. Dancer Kimberly Prosa also served as a double for Portman. She stated: "Natalie took class, she studied for several months, from the waist up is her. Sarah Lane a soloist at ABT, did the heavy tricks, she did the fouéttes, but they only had her for a limited time, a couple of weeks, so I did the rest of whatever dance shots they needed.".
In addition to the soloist performances, members of the Pennsylvania Ballet were cast as the corps de ballet, backdrop for the main actors' performances.Also appearing in the film are Kristina Anapau, Toby Hemingway, Sebastian Stan, and Janet Montgomery.