Several maturity indices were evaluated for in-vessel co-composting of chicken manure and pine sawdust with three different biochars. All the seven mixtures (piles) contained chicken manure and sawdust. Six of these piles contained biochar; each biochar was added at two rates, 5% and 10% wet weight. The maturity of composts was assessed by C/N, dissolved organic carbon (DOC), seed germination, NO3--N/NH4+-N, and the Solvita test. The C/N values of finished composts were from 31.5 to 35.7, which were much higher than the optimum value of 21 for matured compost. Nevertheless, the rest of the parameters indicated that the composts were matured. The C/N values were high because of the high amount of recalcitrant carbon present in the feedstocks: biochar and sawdust. Biochar treated piles showed higher respiration as well as decomposition of DOC indicating higher microbial activity. Use of biochar in composting may reduce NH3 emission and nitrate leaching.