In this work, spent mushroom substrate (SMS) was co-pyrolyzed with oil shale semi -coke (OSS) to investigate the effects of the OSS on yield and chemical compositions of bio-oil product. Oil shale semi -coke was mixed with biomass in the OSS/SMS mass ratios of 0:1, 1:4, 1:1, 4:1 and 1:0. The pyrolysis experiment was carried out by using a lab -scale pyrolysis reactor. The experimental results showed that the addition of the OSS led to an increase of bio-oil yield. The maximum of bio-oil yield was obtained at the OSS/SMS mass ratio of 1:1. The characteristics of the obtained oils were studied by elemental analyzer, FTIR and GC MS. It was found that the bio-oil obtained from the pyrolysis of mixed SMS and OSS had higher carbon and hydrogen content, lower oxygen content than those produced by the pyrolysis of biomass alone. Moreover, there were more aromatics and aliphatic compounds in the obtained bio-oil product. These variations indicated that the existence of the OSS significantly influenced the chemical compositions of bio-oil. (C) 2017 Elsevier Ltd. All rights reserved.