Rats eat kaolin after treatment with poisons or rotation. Thus, eating of nonnutritive substances such as kaolin, so-called pica, is an illness-response behavior of rats analogous to vomiting in humans. For use of rotation-induced pica as a behavioral index of motion sickness in rats we examined what kind of rotation was effective for inducing pica in rats and whether the vestibular apparatus was necessary for its induction. Rats ate much kaolin after double rotation with continuously changing centrifugal and angular accelerations, but little after single rotation with no accelerative changes. However, even double rotation failed to induce pica in bilaterally labyrinthectomized rats. Thus, rotation-induced pica in rats was induced in the same way as motion sickness in humans, suggesting that it resulted from motion sickness in rats. We conclude that pica can be used as a behavioral index of motion sickness in rats.