<p>This study investigates the effectiveness of caffeine and tannin as alternative preservatives for oriented strand board (OSB) panels, focusing on their leaching, fungal decay resistance, and fire performance. Untreated, caffeine-treated, tannin-treated, and industrial reference panels were subjected to standard tests of these performance features. The leaching results indicated that the caffeine-treated panels retained a similar level of chemical content and exhibited lower mass loss after leaching compared to the tannin-treated panels, suggesting a higher concentration of caffeine remained in the panels following the leaching test. Both caffeine and tannin treatments significantly reduced fungal decay caused by <i>T. versicolor</i>, <i>C. puteana</i>, and <i>G. trabeum</i> compared to untreated and industrial reference panels, with caffeine-treated panels demonstrating superior protection among all tested treatments. Fire resistance tests showed that most of the leached panels exhibited longer times to ignition than non-leached panels. However, non-leached panels had higher peak heat release rates. The study concludes that caffeine and tannin treatments effectively protect against fungal decay, but their impact on fire resistance remains inconclusive, with no clear enhancement. These findings highlight the potential of caffeine and tannin as natural wood preservatives, particularly in conditions where decay is a primary concern, though further research is needed to optimize their performance under various environmental conditions.</p>