The process parameters affecting peroxyacetic acid delignification, i.e. temperature, pH and chemical charge, were studied in relation to their effect on carbohydrate depolymerization and dissolution for a softwood kraft pulp. Carbohydrate reactions were found to follow different paths in different pH regions. At low pH, acid hydrolysis was probably the main reason for carbohydrate depolymerization and dissolution. At neutral pH, however, carbohydrate depolymerization was probably caused by the decomposition products of peroxyacetic acid. Peroxyacetic acid may also react with dissolved monosaccharides to form aldonic acids with corresponding and shorter carbon chain lengths as well as aldoses with shorter carbon chains. These reactions were verified through model compound studies. Because of these reactions the amount of carbohydrates in spent liquor is not equal to that removed from pulp fibres during the treatment. These side reactions also consume a small amount of peroxyacetic acid during pulp bleaching.