Poly (lactic-co-glycolic acid) (PLGA) is one of the most successful polymers for sustained parenteral drug products in the market. However, rational selection of PLGA in the formulations is still challenging due to the lack of fundamental studies. The present study aimed to investigate the influence of donepezil (DP) on the in-vitro and in-vivo performance of PLGA sustained microspheres. Three kinds of PLGAs with different end groups and molecular weights were selected. Then DP-loaded PLGA microspheres (DP-MSs) with similar particle size, drug loading, and encapsulation efficiency were prepared using an o/w emulsion-solvent evaporation method. Laser diffraction and scanning electron microscopy showed that the prepared DP-MSs were about 35 μm and spherical in shape. Differential scanning calorimetry and X-ray diffraction indicated that DP was in an amorphous state inside the microspheres. Unexpectedly, the molecular weight and end group of PLGAs did not significantly influence the in-vitro and in-vivo performance of the DP-MSs. The gel permeation chromatography indicated that the degradation rates of PLGAs were accelerated with the incorporation of DP into the microspheres, and the molecular weight of all three kinds of PLGAs sharply dropped to about 11,000 Da within the initial three days. The basic catalysis effect induced by DP might be responsible for the accelerated degradation of PLGAs, which led to similar in-vitro release profiles of DP from different PLGA matrices. A point-to-point level A correlation between the in-vitro release and the in-vivo absorption was observed, which confirmed the accelerated release of DP from the DP-MSs in-vivo. The results indicated that the influence of DP on the degradation of PLGA should be considered when developing DP-sustained microspheres.