The kinetics of cellular precipitation at the grain boundaries in a Cu-3 w/o Ti alloy was investigated using the Johnson-Mehl-Avrami (JMA) model. The experimental results are well described by Cahn's site saturation model, showing that the initiation of cellular colony precipitation is limited by the availability of the nucleation sites. Orientation imaging microscopy (OIM) and transmission electron microscopy (TEM) analyses show that not all high angle grain boundaries contain preferred nucleation sites. It was observed that grain boundaries in aged alloys that do not have cellular colonies tend to have a special coincident site lattice (CSL) relationship.