This study evaluated the effects of a number of chemicals on the physical and mechanical properties and fire, decay, and termite resistance of oriented strandboard (OSB) panels. Disodium octaborate tetrahydrate (DOT), boric acid (BA), melamine phosphate (NIP), and a BA/DOT mixture were sprayed onto the furnish at varying concentrations. The panels were tested for thickness swell, water absorption, modulus of rupture, modulus of elasticity, and internal bond strength according to the procedures defined by ASTM D 1037. All treated panels, except those treated with BA/DOT, were found to comply with CSA 0437 requirements for mechanical properties at a 2 percent concentration level. However, thickness swell and water absorption values were higher compared to CSA 0437 standard values. Laboratory decay tests showed that treated OSB specimens were well protected from both a brown-rot fungus (Fomitopsis palustris) and a white-rot fungus (Trametes versicolor). Weight losses in MP-treated OSB specimens were higher than those in boron-treated specimens. However, increased NIP content caused a decrease in weight loss. In termite tests, BA and DOT were more effective than NIP against Coptotermes formosanus. Contrary to decay test results, OSB specimens containing higher NIP concentrations showed lower resistance against termite attack. In a limited series of cone calorimeter tests, treatments did not substantially improve the fire performance of OSB. Of the treatments studied, the highest retentions of BA and BA/DOT provided some improvement in fire performance. DOT also provided some improvement but it was not commensurate with the amount of chemical added.