Potassium citrate (KCitrate) may improve calcium balance by conferring an alkali load. Calcium supplementation slows postmenopausal bone loss by inhibiting parathyroid hormone (PTH) secretion. This study explores whether combined treatment with KCitrate and calcium citrate (CaCitrate) is more effective than either agent alone in inhibiting bone loss. In a crossover study involving 18 postmenopausal women, the following treatments were compared: KCitrate (4.3 g or 40 mmol/day), CaCitrate (800 mg or 20 mmol calcium/day), combined treatment, and placebo. During the last 2 days of each 2-week phase, serum and 24-hour urine were collected for assessment of calcium metabolism, alkali load, and bone turnover markers. Compared with placebo, KCitrate provided an alkali load and significantly decreased urinary calcium (UCa) without changing serum PTH (sPTH) or bone turnover markers. CaCitrate significantly increased absorbed calcium, marginally decreased sPTH, and significantly reduced bone resorption markers. Combined treatment retained key features of KCitrate and CaCitrate. However, more alkali was delivered than with KCitrate alone, and absorbed calcium did not differ from CaCitrate alone. Compared with placebo, combined treatment increased UCa, marginally reduced sPTH, provided a clear alkali load, and reduced the bone resorption markers serum type I collagen C-telopeptide and urinary N-telopeptide by 20.4% (P < 0.0001) and 18.2% (P = 0.005), respectively. A significant trend was noted for the decrease in bone resorption markers as treatment changed from placebo to KCitrate to CaCitrate to combined treatment. In postmenopausal women, combined treatment with KCitrate and CaCitrate inhibits bone resorption by providing an alkali load and increasing absorbed calcium.