The present invention provides a method for producing an osteopenia animal model by RANKL administration and an osteopenia animal model.Also, a method for producing an osteopenia animal model, comprising administering soluble RANKL or a fused protein of soluble RANKL with an epitope tag to a non-human animal so as to promote vivo osteoclast differentiation and activation in the non-human animal, and an osteopenia animal model produced by the method are provided.