<b>Introduction:</b> Investigations in rodents as well as in vitro experiments have suggested an anabolic influence of specific collagen peptides (SCP) on bone formation and bone mineral density (BMD). The goal of the study was to investigate the effect of 12-month daily oral administration of 5 g SCP vs. placebo (CG: control group) on BMD in postmenopausal women with primary, age-related reduction in BMD. <b>Methods:</b> 131 women were enrolled in this randomized, placebo-controlled double-blinded investigation. The primary endpoint was the change in BMD of the femoral neck and the spine after 12 months. In addition, plasma levels of bone markers-amino-terminal propeptide of type I collagen (P1NP) and C-telopeptide of type I collagen (CTX 1)-were analysed. <b>Results:</b> A total of 102 women completed the study, but all subjects were included in the intention-to-treat (ITT) analysis (age 64.3 ± 7.2 years; Body Mass Index, BMI 23.6 ± 3.6 kg/m²; T-score spine -2.4 ± 0.6; T-score femoral neck -1.4 ± 0.5). In the SCP group (<i>n</i> = 66), BMD of the spine and of the femoral neck increased significantly compared to the control group (<i>n</i> = 65) (T-score spine: SCP +0.1 ± 0.26; CG -0.03 ± 0.18; ANCOVA <i>p</i> = 0.030; T-score femoral neck: SCP +0.09 ± 0.24; CG -0.01 ± 0.19; ANCOVA <i>p</i> = 0.003). P1NP increased significantly in the SCP group (<i>p</i> = 0.007), whereas CTX 1 increased significantly in the control group (<i>p</i> = 0.011). <b>Conclusions:</b> These data demonstrate that the intake of SCP increased BMD in postmenopausal women with primary, age-related reduction of BMD. In addition, SCP supplementation was associated with a favorable shift in bone markers, indicating increased bone formation and reduced bone degradation.