Background: Eldecalcitol (ELD) and denosumab are some of the most common therapeutic options for osteoporosis management. ELD effectively increases bone mineral density (BMD) in osteoporotic patients, independent of baseline vitamin D status or calcium intake. However, the efficacy of denosumab combined with either ELD or native vitamin D plus calcium in postmenopausal Chinese women with osteoporosis has not been established. Methods: In this single-center, randomized, open-label, active-controlled clinical trial, postmenopausal women with osteoporosis (defined as a BMD T-score ≤ −2.5 at the lumbar spine [LS], total hip [TH], or femoral neck [FN], or low bone mass with fragility fracture history) were enrolled from Xi’an Honghui Hospital in China and randomized 1:1 to two 12-month treatment regimens: the ELD group received ELD (0.75 μg orally daily) combined with denosumab (60 mg subcutaneously every 6 months), while the control group received the same denosumab regimen plus native vitamin D (800 IU orally daily) and calcium (600 mg orally daily). The primary endpoint was the 12-month percent change in LS BMD from baseline. Secondary endpoints included changes in FN- and TH-BMD from baseline, bone turnover markers, serum parathyroid hormone, quality of life, and the incidence of new fractures. Results: Of the 100 randomized participants, 45 in the ELD group and 46 in the control group were included in the efficacy analysis. After 12 months of treatment, LS-BMD increased significantly in both groups (both p < 0.05), with a greater increase in the ELD group than in the control group (6.75% vs. 4.99%), yielding a statistically significant between-group least-squares mean difference of 1.75% (95% CI, 0.10 to 3.41; p = 0.038). The reduction in serum β-CTX was significantly smaller in the ELD group than in the control group at 3 months (91.00% vs. 93.62%, p = 0.002), with no significant between-group differences thereafter. Seven fractures were reported (one non-vertebral in the ELD group; one vertebral and five non-vertebral in the control group). No significant between-group differences in FN- or TH-BMD, quality of life, or overall adverse event rates were observed. Both regimens were generally well-tolerated, without clinically meaningful calcium-related safety signals. Conclusions: Combination therapy with denosumab and eldecalcitol improved LS-BMD more effectively than denosumab with native vitamin D and calcium in postmenopausal Chinese women with osteoporosis. Clinical trial number: ClinicalTrials.gov identifier NCT05884372, registered on 1 June 2023.