It is a normal practice in oriented strandboard (OSB) production to store logs outdoors for a period of time prior to the flaking process. The duration of yard storage depends on harvest season and sources of log supply. Outdoor log storage without protection could change the mechanical and chemical properties of wood due to attack by various fungi. To understand how outdoor log storage affects the wood and subsequently the strandboard quality, two piles of aspen logs were set up outside and stored for a period of four months (July 9 to November 14, 2001). One of the piles was treated with a biological solution to prevent fungal growth. The other one was stored without such treatment. Both piles contained non-debarked and partially debarked logs. Evaluation of sap stain development indicated that all logs had been colonized by staining fungi with an average stain coverage of 9.37 to 57.18% and maximum stain penetration of 3.58 to 7.27 cm over the log cross-section. The variation of fungal colonization depended on log treatment and bark condition. The most effective way to prevent stain growth was with the combination of biological treatment and partial debarking. This was followed in effectiveness by biological treatment and no debarking, no treatment and partial debarking, and, finally, no treatment and no debarking. A series of strandboard was prepared from fresh and aged aspen logs. It was observed that all boards made from stored logs were statistically comparable to or superior to the control boards made from fresh aspen logs. The boards made from treated/partially debarked and untreated/non-debarked logs were statistically comparable to each other except for the higher wet MOR for the former. In addition, both board types were stronger than other boards in terms of IB and water resistance. Compared to control boards, the stronger boards in terms of water resistance were also made from biologically treated/non-debarked and untreated/partially debarked logs. Some individual stained strands were observed on the finished board surface, which could affect board appearance if the wood had been highly attacked by fungi. Less staining was found in the boards prepared from biologically treated and partially debarked logs, as compared to other stored logs.