In order to determine the effect of different drying conditions on the quality of timber, small diameter plantation grown Birch （Betula platyphylla and B. costata） logs were either air dried or kiln dried. Property indexes such as dimensional stability, deformation degree, hardness and cleavage strength were tested and the results were analyzed. According to the data, the authors found that the quality of the logs that were kiln-dried was better than those that were air-dried. They also found there were differences in properties in the kiln-dried logs dried under different drying schedules. A milder schedule based on relatively lower temperature and higher humidity could bring better drying quality. From the results, the authors concluded that kiln drying small diameter plantation grown timber produced better results than air drying.