[Objective] To evaluate the clinical value of diagnosing osteoporosis with vertebra bone mineral density(BMD) by measurement with quantitative computed tomography (QCT) . [ Method] BMD in of lumbar vertebrae (L<,1～4>)were measured by QCT in 53 healthy middleaged persons or elderly persons (group A) and 68 osteoporosis patients ( groupB) . [Result] BMD in group A declined obviously as age increasing with significant differences (P<0. 01) . In group B,all 68 patients showed osteoporosis according to the diagnostic standard of BMD≤x -2. OSD. Sixty patients showed osteoporosis ifthe diagnostic standard was set to BMD ≤ x -2. 5SD. The BMD values of different age group was lower than the bone quantityblock values. [Conclusion] As a method for diagnosing osteoporosis, QCT has advantages of high sensitation, being precise,being reproducible and is easy for applying. It would be more practical and could decrease mis - diagnosing if the diagnosticstandard was BMD≤x-2.OSD.