From a technology basis, biological processes appear to be the main treatment alternatives for nitrogen removal from animal wastes (Germili et al., 1993). Effluent characterisation is the first stage in assessing the biological treatment strategy. For biological nitrogen removal treatment, the characterisation of influent organic matter amount and quality is of primary importance, because these variables are related to the denitrification kinetics and the oxygen requirements. A fractionation of the effluent organic content as regard to its biodegradability is thus required. Wastewater organic matter fractionation, expressed in Chemical Oxygen Demand (COD) units, was first developed for municipal wastewater characterisation (Henze, 1992; Orhon et al., 1997; Spérandio and Paul, 2000). More recently, it has been applied to some industrial wastewaters (Orhon et al., 1995). Piggery wastewater is a very strong waste compared to domestic wastewater and only very few data have been reported on pig slurry COD fractionation in the literature (Andreottola et al., 1997). To overcome this shortfall, the present study aimed at (i) developing a procedure, based on domestic and industrial wastewater knowledge, to determine COD fractions in piggery wastewaters, and (ii) collecting experimental data on piggery wastewater COD fractions.