This Study was carried out to investigate the course of air-drying and drying defects of red pine (Pinus densiflora S. et Z.) and Italian poplar (Populus eurameriana I-476) boards 1,2 and 3cm thick in the flat pile. The results are as follows. 1. Air-drying curves for red pine and Italian poplar boards were same as figure 1 and 2. These moisture contents were lower in July and August during seasoning periods. 2. Air drying time of red pine board required to dry 15 percent moisture content in one week for 1 cm board, five weeks for 2 cm board and six weeks for 3cm board respectively. In case of Italian poplar boards, in one week for 1 cm board, four weeks for 2 cm and five weeks for 3 cm board. The thickness of board influenced the time for air drying. 3. Drying defects such as checking, warping and staining happened badly in pine than in Italian poplar boards. Especially, checking was severe in thicker board and warping in thinner board.