Co-composting spent pig (Sus scrofa L.) litter (a mixture of partially decomposed pig manure and sawdust) with pig sludge (the sludge that settled at the bottom of the primary sedimentation tank in treating slurries) was evaluated as a means to reduce the volume of wastes and to produce a stable organic soil amendment. Three piles with forced-aeration were established by mixing 2:1 wet (v/v) ratio of spent litter and pig sludge. Composting process parameters monitored over 91 days included some physical, chemical, and biological properties of the spent litter-sludge mixture. The efficiency of composting at the top location of the forced-aeration piles was slower than the middle, bottom and surface locations. The top location took 63 days to return to ambient level. It took 49 days for the middle and bottom locations, and only 28 days were needed for that in the surface location. The variations in temperature at different locations of the forced-aeration piles were also reflected in differences in some chemical and biological parameters. The top location had the lowest total aerobic heterotroph numbers, suggesting that the microbial activity was slower. Moreover, this zone also had the lowest germination index and highest concentrations of NH4+-N and water-extractable Cu and Zn during the first 49 days of composting, indicating that the elimination of phytotoxicity and the composting rate was slower than the middle, bottom and surface locations. However, these differences were evident only during the first 49 days of composting. By day 63, the spent litter-sludge at the top location had similar properties with that of the other three locations.