Post-pregnancy osteoporosis is not a common disease and is hard to diagnosis because their specific situation is post-partum and lactation. It commonly occurs on lumbar spine within a few months after the birth of a patient's first child and it could lead to be fracture after minor trauma. Although its etiology is not clear, it would not be of sufficient magnitude to cause fractures unless the woman already had a substantial decrease in bone mass. Also, it is rare to be combined with ankylosing spondylitis. Ankylosing spondylitis has a higher risk of osteoporosis and vertebral fracture which increased with the duration of disease. We report a case of post-pregnancy osteoporosis with multiple spinal compression fracture in association of ankylosing spondylitis.