We present elemental abundance ratios for red giant stars in 9 old halo globular clusters based on the homogeneous data sample and analysis method. Our result suggests that [Si/Ti] ratios in old globular clusters decrease with Galactocentric distances, confirming the previous result by Lee & Carney (2002). We propose that contributions from different masses of the Type II suprenovae progenitors that enriched proto-globular clusters' clouds are responsible for this gradient.