The effect of salicylic acid and its derivatives on the properties of phenolic resin composites was evaluated. The composites were reinforced with aluminum oxide particles in both solid and hollow forms. Differential scanning calorimetry studies have shown that the reaction rate of phenolic resin was accelerated by salicylic acid, but was not affected by the other compounds. Salicylic acid also reduced the flexural strengths of the phenolic resin composites. The strength was decreased by more than 30% in comparison to that with no acid added. In contrast, two derivatives of this acid-sodium salicylate and 4-hydroxybenzoic acid-have minimal impact on the flexural strengths of the composites. (C) 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 642-647, 2000.