During the period from January to September 1995, 1.010 Women(premenopausal 466 cases and postmenopausal 544 cases) of employees and family member were observed for bone mineral density of lumbar spine using Dual Energy X-ray Absorptiometry(DEXA) at Medical Department of Korea Life Insurance Co. Ltd. Results obtained were as follows: 1) In premenopausal women 466 cases, the ratio of decreased bone mineral density of lumbar spine according to age groups shows 3rd decade were 5 cases(9.80%) among 51 cases, 4th decade were 31 cases(8.68%) among 357 cases, and 5th decade were 10 cases(17.24%) among 58 cases. 2) In postmenopausal women 544 cases, the ratio of decreased bone mineral density of lumbar spine according to age groups shows 3rd decade were 2 cases(66.67%) among 3 cases, 4th decade were 28 cases(31.11%) among 90 cases, 5th decade were 168 cases(48.70%) among 345 cases, 6th decade were 73 cases(73.0%) among 100 cases, and 7th decade were 4 cases(66.67%) among 6 cases. 3) Bone mineral density begins to decrease with age as early as the 4th decade, even in the premenopausal state. In the 4th decade, premenopausal women exhibit an average 8.68% decrease in bone density. Postmenopausal women in this same age group, however, demonstrate an average bone density decrease of 31.11%.