Microporosity and granules size are important parameters for the development of suspension, composites and injectable bone substitutes. In this experimental study performed in a rat bone model of critical size defects, were have determined the kinetics of bioceramic resorption and bone ingrowth. Two kinds of granules (1mm in diameter) of Biphasic Calcium Phosphate BCP (60/40 HA/TCP ratio) with 20% and 40% microporosity of less of 5 microns in size, were used. Higher bone ingrowth was observed for low porosity (LP) at 3 weeks versus high porosity (HP); the contrary was measured after 6 weeks. About the kinetics of BCP resorption, significant difference between the 2 porosities was noticed, the higher for high microporosity. High porosity on time, promotes more bone ingrowth at the expense of the bioceramic than lower microporosity.