Due to the practical advantages of fermenting the carbohydrate-rich cereal component of fermented feeds separately and combining it with the protein-rich components just before feeding (Beal et al., 2005; Moran et al., 2006), it is desirable to have a high lactic acid concentration in the fermented cereal component so as to minimise the dilution effect on the acid concentration and pH of the feed when mixed with the protein-rich component at feeding. With the same cereal substrate and lactic acid bacteria (LAB), a key factor that might influence lactic acid production is the particle sizes produced at milling which could affect the amount of sugars available for microbial enzymatic fermentation. Further more, Anguita et al. (2006) indicated that technological processing of ingredients promotes higher starch hydrolysis in addition to increasing the amount of soluble non-starch polysaccharides and modifications in the physicochemical properties depending on the nature of the feed ingredients. The present study was designed to investigate the effect of particle size on fermentation of sorghum for poultry feed.