The use of aromatase inhibitor (AI) in postmenopausal women with hormone receptor (HR)-positive early breast cancer (EBC) produces a deleterious effect on bone mass and an increase in fractures. Several studies using intravenous bisphosphonates have shown effective management of AI-induced bone loss. To determine whether a lower dosage in oral form combined with calcitriol can effectively manage AI-induced bone loss, we performed a randomized, double-blind, prospective, placebo-controlled 24-week trial with a combination of alendronate and 0.5-μg of calcitriol daily to HR-positive EBC patients. A total of 98 Korean postmenopausal women with HR-positive EBC who received daily AI, calcium and vitamin D were randomly assigned to 5-mg of alendronate and 0.5-μg of calcitriol (Maxmarvil^®) or placebo groups. The bone mineral density (BMD) and turnover markers were measured. At week 24, the difference in lumbar BMD between the groups was 3.0% (p < 0.005). The increase in C-telopeptide after 24 weeks was significantly less in the Maxmarvil group compared to that in the placebo group (35.2 ± 17.5% vs. 109.8 ± 28.6%, p < 0.05). Our study demonstrates that a combination of 5-mg alendronate and 0.5-μg calcitriol is effective to prevent bone loss due to AI in Korean postmenopausal women with EBC.