To improve dispersibility of silica nanoparticle in organic solvents, the grafting of poly(L-lactide) (PLLA) onto silica nanoparticle surface by ring-opening polymerization of L-lactide (LA) was investigated in the presence of an amidine base catalyst. The ring-opening polymerization of LA successfully initiated in the presence of silica having amino groups (silica-NH2) and an amidine base catalyst to give PLLA-grafted silica, but not in the presence of untreated silica (silica-OH). In the absence of the amidine base catalyst no ring-opening polymerization of LA even in the presence of silica-NH2 and no grafting of PLLA onto silica were observed. It became apparent that the amidine base catalyst acts as an effective catalyst for the ring-opening graft polymerization of LA from the surface of silica-NH2. In addition, it was found that the percentage of PLLA grafting onto silica could be controlled according to the reaction conditions. The average particle size of PLLA-grafted silica was smaller than that of silica-NH2. Therefore, it was considered that the aggregation structure of silica nanoparticles was considerably destroyed by grafting of PLLA onto the surface. The PLLA-grafted silica gave a stable dispersion in polar solvents, which are good solvents for PLLA. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012