Disclosed are: a method for producing an osteopenia model animal by administering RANKL and an osteopenia model animal. Specifically disclosed are: a method for producing an osteopenia model animal, which comprises administering soluble RANKL or a fusion protein of soluble RANKL and an epitope tag to a non-human animal to stimulate the differentiation and activation of an osteoclast in the non-human animal and an osteopenia model animal produced by the method.