the objective of the experiment was to evaluate the bio-conversion treatment to enhance the nutritional value and degradability of cotton textile mill waste, using the fungi pleurotus sajor-caju. the experiment was conducted at the departments of biology and animal science of the universidade federal de lavras (ufla), between july 2002 and january 2003. bio-conversion was induced by the use of the residue as the main component in a substrate bed for cultivation of edible mushrooms (c1 and c2). in comparison to the untreated cotton textile mill waste, two bio-conversion alternatives by pleurotus sajor-caju were tested. after mushroom production, samples of the treated material were submitted to in situ degradability tests and chemical composition. results indicated that c1 and c2 treatments decreased fibrous fractions (adf and ndf) and increased cp of cotton textile mill waste, improving the chemical composition. c1 and c2 treatments also resulted in an increased of soluble fraction (a), the degradation rate (c), and decreased insoluble potential degradable fraction (b); increasing effective degradability of dm and ndf of cotton textile mill waste.