Effect of outdoor storage conditions of wood chip pile on the physical and mechanical properties of wood-based panel, high density fiberboard (HDF), was investigated in this study. The chip pile of Southern pine wood without bark was stored for 6 months at woodyard of a commercial fiberboard manufacturer. The HDFs with dimensions of 2632 mm x 2081 mm x 8 mm were commercially produced from the chips with dimensions of 23-25 mm x 20-22 mm x 3-4 mm at 15, 30, 45, 60, 90, 120, and 180 days of the storage. Some physical and mechanical properties of the HDF panels were determined according to European Norms. The thickness swelling and surface absorption of panels increased as the storage time increased from 15 to 180 days. The modulus of rupture values decreased noticeably after 60 days of the chip storage while this decrement was observed for the modulus of elasticity values after 90 days. The formaldehyde emission values of the panels increased from 8.0 to 9.6 mg per 100 g of absolutely dry panel as the storage time increased. In particular, the internal bond strength significantly decreased (1.71-1.04 N mm(-1)) as the storage duration reached to 180 days. This was mainly caused by a combination of accelerated resin cure and thermal/biological decomposition of the wood chips. Based on the findings obtained from the present study, it can be said that outdoor storage duration of pine chip piles used in the manufacture of HDF panels should not be more than 30 days. (C) 2013 Elsevier Ltd. All rights reserved.