Japanese cedar (Cryptomeria japonica) wood and bark were gasified using an entrained-flow-type gasification reactor at 900 degrees C in the presence of H2O or H2O + O-2. With H2O alone, the cedar wood was gasified well: carbon conversion into gas [CC(g)] = 94.3%; however, cedar bark was not gasified so well: CC(g) = 73.4%, and relatively large amounts of solid residues were produced: carbon conversion into solid residues [CC(sr)] = 14.0%. Gas produced from both cedar wood and cedar bark were suitable compositions for catalytic liquid fuel synthesis: [H-2]/[CO] congruent to 2-3. Tar yields were low: that from the cedar wood was <0.1 wt %, and that from the cedar bark was 0.3 wt %. The tar from the cedar bark contained much more various kinds of compounds. With H2O + O-2, CC(g) was improved (cedar wood, 96.5%; cedar bark, 87.5%) and CC(sr) of the cedar bark decreased (2.6%). A high lignin content in the cedar bark was one of main differences from the cedar wood and was a possible reason for its low CC(g). To examine the effect of the lignin on gasification, organosolv-lignin (o-lignin) and delignified cedar bark were also gasified. The CC(g) of the o-lignin was low, 59.9%, with H2O alone and increased to 81.4% with H2O + O-2, whereas that of the delignified cedar bark was high, 95.4%, with H2O alone and increased to 103.6% with H2O + O-2. The Japanese cedar wood, cedar bark, delignified cedar bark, and o-lignin were thermogravimetrically analyzed in He with H2O or H2O + O-2. Their decompositions proceeded more in He with H2O + O-2 than with H2O. We ordered them according to easiness of decomposition: delignified bark > wood > bark > o-lignin, in all of these atmospheric conditions. Effects of feedstock and atmosphere on the gasification and thermogravimetric analyses had the same tendencies. We, therefore, concluded that the lower CC(g) of the cedar bark than the cedar wood was attributable to difficulties of gasifying the lignin components.