This study investigated the effect of particle size and chemical composition of grape seed flour (GSF) on the physical, chemical and sensory quality of cookies. Results indicate that the chemical composition of GSF varied significantly with particle sizes and smaller particle fraction had higher ash, fat, protein and extractible polyphenol contents but lower dietary fiber. Inclusion of 2.5-10% GSF in the cookie formula enhanced darkening, increased thickness and hardness, increased polyphenol and dietary fiber contents in dose-dependent manner, but reduced diameter and consumer acceptability of cookies to various degrees. The impacts of GSF on the cookie quality and sensory properties were strongly associated with the inclusion level and particle size of GSF. Higher GSF (5%) inclusion and smaller GSF particle size (104 µm) resulted in lower consumer acceptability. To minimize the undesirable effect of GSF on cookie quality, up to 5% of GSF with average particle size 209 µm is recommended.