In order to develop 2-hour-fireproof cross laminated timber （CLT） floor and wall structures, covering them with wood impregnated with fire-retardant agent was studied. In the fire test of the CLT wall specimen, two layers of fire-retardant impregnated wood （(cid:9479)(cid:9526)(cid:9533)(cid:9524)(cid:9528)(cid:9523)(cid:9521)(cid:9513)(cid:9526)(cid:9517)(cid:9509)(cid:9444)(cid:9518)(cid:9509)(cid:9524)(cid:9523)(cid:9522)(cid:9517)(cid:9511)(cid:9509) D. Don） were al-ternately laminated with screws to the load-bearing CLT and a fire test was conducted for 2 hours. The total thickness of the covering material was 90 mm. However, the CLT burned due to early drop-off of the top layer and shrinkage of the second layer, and the wall specimen did not show 2-hour fire-resistance performance. Based on this test result, in the fire test of the floor, the covering material was specified as a fire-retardant