Dried and ground brewer's spent grain (BSG) was blended with soft wheat flour at levels of 5-25%. BSG preparations of fine (<212 mum). medium (212-425 mum) and coarse (425-850 mum) particle sizes were used in the production of wire-cut cookies. The protein content decreased and the dietary fibre content (acid detergent fibre, neutral detergent fibre and total dietary fibre) increased, as the particle size of the BSG samples increased. The results indicated that BSG preparations with high dietary fibre content have potential as a source of dietary fibre. The effects of BSG on the quality and dietary fibre content of cookies have been investigated. Total dietary fibre (TDF) contents of the cookies supplemented with different particle size BSG increased significantly (p<0.05) as the addition level increased. Cookies prepared with BSG of medium and coarse particle sizes resulted in better properties in terms of Spread Ratio, Hunter color values and overall sensory score as compared to those made with BSG of fine particle size. Cookies made with medium and coarse particle size BSG gave better cookie properties up to the 15% addition and deteriorated significantly above this level (p<0.05).