Postmenopausal osteoporosis occurs due to estrogen deficiency, which leads to bone loss. There are evidences linking osteoporosis to increased oxidative stress, and studies have indicated an association between osteoporosis and changes in markers of oxidative stress, such as glutathione peroxidase (GPx). Calcium supplements are usually prescribed in the prevention and treatment of osteoporosis. The objective of this study was to investigate the influence of bone disease and calcium supplementation on glutathione peroxidase (GPx) activity and bone mineral density (BMD). Besides, we also evaluated the relationship among BMD and age, GPx activity and lactation time. Postmenopausal women (n=70) were selected from Santa Maria University Hospital and divided into six groups, according to bone densitometry: (1) healthy, no calcium supplementation, (2) healthy, calcium supplementation, (3) osteopenia, calcium supplementation, (4) osteopenia, no calcium supplementation, (5) osteoporosis, calcium supplementation and (6) osteoporosis, no calcium supplementation.  Blood GPx activity was measured using a spectrophotometric method. Patientes with osteopenia and osteoporosis had higher GPx activity than healthy woman (24.47 ± 0.93 and 32.01 ± 2.12 vs 19.20 ± 1.20 mmol NADPH/g Hb/ min, p<0.05). Calcium supplementation reduced GPx activity (26.31 ± 1.54 vs 23.32 ± 1.26 mmol NADPH/g Hb/ min of the non supplemented groups, p<0.05). Multiple regression analyses showed that GPx activity was negatively correlated (β = -0.49, p < 0.01) with lombar bone mineral density (BMD) but  positively correlated (β = 0.23, p < 0.01) with lactation time. There were no relationship between BMD and age or lactation time neither between GPx and age.  Our results suggest that GPx activity is affected by bone disease as much as calcium supplementation in postmenopausal women.