Objective:Postmenopausal women with breast cancer are at increased risk of bone loss because of age related estrogen deficiency face which accelerated with the use of aromatase inhibitors(AIs).We aimed to study the effect on bone mineral density(BMD) and bone formation biomarker osteocalcin level in postmenopausal breast cancer patients,for the first three years of adjuvant hormonal treatment of both groups Tamoxifen versus Anastrozol.Methods:One-hundered postmenopausal breast cancers were prospectively randomized to receive either Tamoxifen 20 mg/day(n = 50) or Anastrozole 10 mg(n = 50).Both BMD and osteocalcin were assessed initially before treatment and then at regular intervals for both groups.Results:Use of Tamoxifen was associated with significant annual decrease in osteocalcin(P = 0.001),whereas Anastrozole group had gradual increase of the annual levels(P < 0.01).BMD decreased significantly in Anastrozole versus Tamoxifen groups(2.6% vs.0.4%,P < 0.001).Osteoporosis T <-2.5 was reported significantly higher in Anastrozole group(P < 0.01).Women with initial osteopenia in Anastrozole group showed significant decrease in BMD(P < 0.05).The addition of bisphosphonate for patients with early osteoporosis markedly improved both osteocalcin level and BMD.Conclusion:Tamoxifen preserves BMD in postmenopausal breast cancer patients,whereas Anastrozole accelerates age associated fall in BMD especially in the first year of therapy,moreover,the addition of bisphosphonate can help to decrease the skeletal related events associated with treatment to ensure better quality of life with treatment. Objective: Postmenopausal women with breast cancer are at increased risk of bone loss due of age-related estrogen deficiency face which accelerated with the use of aromatase inhibitors (AIs) .We aimed to study the effect on bone mineral density (BMD) and bone formation biomarker osteocalcin level in postmenopausal breast cancer patients, for the first three years of adjuvant hormonal treatment of both groups Tamoxifen versus Anastrozol. Methods: One-hundered postmenopausal breast cancers were prospectively randomized to receive either Tamoxifen 20 mg / day (n = 50) or Anastrozole 10 mg (n = 50) .Both BMD and osteocalcin were initially defy before treatment and then at regular intervals for both groups. Results: Use of Tamoxifen was associated with significant annual decrease in osteocalcin (P = 0.001), whereas Anastrozole group had gradual increase of the annual levels (P <0.01) .BMD decreased significantly in Anastrozole versus Tamoxifen groups (2.6% vs.0.4%, P <0.001) .Osteoporosis T <-2.5 was reported significantly higher in Anastrozole group (P <0.01) .Women with initial osteopenia in Anastrozole group showed significant decrease in BMD (P <0.05). The addition of bisphosphonate for patients with early osteoporosis markedly improved both osteocalcin level and BMD. Conflusion: Tamoxifen preserves BMD in postmenopausal breast cancer patients, an Anastrozole accelerates age associated fall in BMD especially in the first year of therapy, moreover, the addition of bisphosphonate can help to decrease the skeletal related events associated with treatment to ensure better quality of life with treatment.