The effect of particle size and phosphorous content in biomineralization media on in vitro bioactivity of monticellite based ceramic powders was investigated. Monticellite based ceramic powder was synthesized at 800 degrees C for 4 h using boron derivative waste. Monticellite based ceramic powder, comprising monticellite, akermanite, diopside, calcium magnesium borate and zeolite LTA crystalline phases, was crushed and then ball-milled for optimized time to obtain lowest average particle size and the narrowest particle size distribution. In vitro bioactivity of both coarse (d10: 0.5 mu m, d50: 3.0 mu m, d90: 42 mu m) and fine (d10: 0.5 mu m, d50: 1.4 mu m, d90: 4.8 mu m) wafers was determined by incubation in Lactated Ringer's Solution and Human Blood Plasma for 1, 3, 5, 7, 14, 21 and 28 days at 36.5 +/- 0.5 degrees C. The obtained results exhibited that calcite (CaCO3) layer after immersion in Lactated Ringer's Solution and bone-like apatite layer after immersion in Human Blood Plasma were formed on the surface of coarse and fine wafers. The presence of phosphorus in biomineralization media is necessary for apatite formation. The increment of surface roughness favors homogeneous nucleation, and fasten nucleation and growth kinetics of precipitation. As a result, the bioactive characteristic of monticellite based ceramic powder could be governed by the particle size. (C) 2020 SECV. Published by Elsevier Espana, S.L.U.