Vermistabilization of paper mill wastewater sludge (PMS) spiked with cow dung (CD) at ratios of 0%, 25%, 50%, 75%, and 100% was carried out employing the earthworm, Eisenia fetida. A total of five treatments were established and changes in chemical and microbial properties of mixtures were observed. Vermistabilization caused decreases in total organic carbon, C:N ratio and cellulose by 1.2-1.5,4.6-14.6, and 2.3-9.7-fold, respectively, but increases in pH, electrical conductivity, ash content, N-tot, P-avail, P-tot, K-exch, Ca Na, and N-NO3- of 1.06-1.11, 1.2-1.6, 1.3-1.6, 3.8-11.5, 4.1-6.5, 5.7-10.3, 1.7-2.0, 1.16-1.24, 1.23-1.45, 4.2-13.4-folds, respectively. PMS with 25-50% of CD showed the maximum mineralization rate. The fungal, bacterial and actinomycetes population increased 2.5-3.71, 3.13-8.96, and 5.71-9.48-fold, respectively after vermistabilization. The high level of plant-available nutrients indicates the suitability of vermistabilized material for agronomic uses. (C) 2012 Elsevier Ltd. All rights reserved.