In intensive farming areas, the design of biological nitrogen removal plants for piggery wastewater requires a better understanding of the biodegradability of the effluent. For this purpose, an experimental procedure based on ultimate BOD tests and respirometry was developed to quantify the soluble (SI) and particulate (XI) inert organic fractions, and the readily (SS) and slowly (XS) biodegradable organic fractions contained in piggery wastewater.For the four wastewaters tested, the SI and XI fractions were equal to 3-4 gO2.l-1 and 17-28 gO2.l-1, respectively, which resulted in a total inert fraction of 42 to 84% of total COD. The SS and XS fractions were very variable, ranging 0-5 gO2.l-1 and 4-25 gO2.l-1 respectively, depending on the farm management practices and the storage conditions prior to biological treatment. From these results, the denitrification potential of the piggery wastewaters could be assessed. Despite of the high COD content of the four wastewaters, only two wastewaters had a sufficient Total biological oxygen demand / Ammonium (TBOD/NH4-N) ratio to allow a complete denitrification. Factors influencing the COD fractions in piggery wastewater should be studied to optimise the design and operation of the treatment plants.