Bioactive glasses have attracted considerable interest in recent years. In this work, Differential Thermal Analysis (DTA) measurements were performed on bulk and powdered samples of the SiO2-Na2O-CaO-P2O5 glass system, in order to study the particle size effect on the crystal growth and nucleation process. A shift of the crystallization peak to lower temperatures and deconvolution of a slightly asymmetric crystallization peak into two separate peaks were observed with decreasing particle size. The bioactive behavior -through the process of immersion SBF- of the specific glass is studied as a function of particle size. A better bioactive response was observed increasing particle size until a specific size, further increase leading in no further improvement in the bioactive behavior.