Cross-laminated timber (CLT) is becoming increasingly adopted into wooden construction of South Korea. Due to the lack of standards and protocol for CLT, there are many problems in the production and utilization phases. This study focused on the deformation and defects of CLT due to humidity variations. In this study, small, cross-laminated specimens were manufactured using three layers of laminated larch planks that had various moisture contents. The dimensional changes of these specimens were measured in response to changing internal conditions including side adhesion or moisture content variation and external conditions such as humidity. Shrinkage in width and thickness was less than 1.0% when using dry planks as the cross-laminated specimen. However, high-moisture content (MC) planks were not suitable when used as the surface layer of the CLT, as the shrinkage in width and thickness were greater than 2.0%. When high-MC planks are used in the inner layer, their shrinkage must be less than 2% to prevent splitting caused by a MC difference between the surface and inner planks. For this purpose, laminates with a MC less than 15% should be used for CLT.