Recent improvements in the management of oil sand tailings used by the Canadian oil sand industry have resulted in the production of composite tailing sands (CT): a new challenging material for reclamation work. Jack pine (Pinus banksiana Lamb.), hybrid poplar (Populus deltoides Bartr. ex Marsh. xPopulus nigra L.) and red clover (Trifolium pratense L.) plants were used in an 8-week greenhouse bioassay to evaluate the mycorrhizal inoculum potential of CT. This inoculum potential was compared with that of three other reclamation materials [common tailing sands (TS), deep overburden (OB) and muskeg peat (MK)], and with three sites reclaimed in 1982 (R82), 1988 (R88) and 1999 (R99). CT was devoid of active mycorrhizal propagules while all other materials showed some level of inoculum potential. Arbuscular mycorrhizal fungi were observed on roots of clover or poplar grown in TS, OB, and all substrates containing peat (MK, R82, R88 and R99). Pine roots were also colonized by vesicle-forming hyphae of an unidentified fine endophyte and by dark septate fungi. Ectomycorrhizas (ECM) were observed on pine and poplar grown in OB, MK, and in soils from the two older reclaimed sites (R82 and R88). Using morpho- and molecular typing, six ECM fungi were identified to the genus or species level: Laccaria sp., Thelephora americana, Wilcoxina sp. (E-strain), Tuber sp. (I-type), a Sebacinoid, and a Pezizales species. Laccaria sp. and Wilcoxina sp. were the most frequently observed ECM species.