beta-Tricalcium Phosphate (beta-TCP), one of the most used bone graft substitutes, may contain up to 5 wt% foreign phase according to standards. Typical foreign phases include beta-calcium pyrophosphate (beta-CPP) and hydroxyapatite (HA). Currently, the effect of small amounts of impurities on beta-TCP resorption is unknown. This is surprising since pyrophosphate is a very potent osteoclast inhibitor. The main aim of this study was to assess the effect of small beta-CPP fractions (<1 wt%) on the in vitro osteoclastic resorption of beta-TCP. A minor aim was to examine the effect of beta-CPP and HA impurities on the physico-chemical properties of beta-TCP powders and sintered cylinders. Twenty-six batches of beta-TCP powder were produced with a Ca/P molar ratio varying between 1.440 and 1.550. Fifteen were further processed to obtain dense and polished beta i-TCP cylinders. Finally, six of them, with a Ca/P molar ratio varying between 1.496 (1 wt% beta-CPP) and 1.502 (1 wt% HA), were incubated in the presence of osteoclasts. Resorption was quantified by white-light interferometry. Osteoclastic resorption was significantly inhibited by beta-CPP fraction in a linear manner. The presence of 1% beta-CPP reduced beta-TCP resorption by 40%, which underlines the importance of controlling beta-CPP content when assessing beta-TCP biological performance.