Resol resin composites reinforced with alkali-treated bamboo strips were fabricated with a hand-lay-up technique. This study was aimed at the evaluation of the influence of the caustic concentration on the mechanical properties of bamboo-strip-rein forced resol composites with a constant 50% loading of the reinforcement. The treatment of bamboo fiber in a Solution of sodium hydroxide with increasing concentration percentages resulted in more and more rigid composites; as a result, the strength and modulus values exhibited improvements. The maximum improvement in the properties was possibly achieved with 20% caustic treated reinforcements. An infrared study indicated the formation of aryl alkyl ether with -OH groups of cellulose and methylol groups Of resol. Beyond 20%, there was degradation in all the strength properties due to the failure of the mechanical properties of the reinforcement itself. A correlation was found to exist between the mechanical properties and the morphology that developed. Another set of composites with variable loadings of 20% alkali treated fiber (40, 50, and 60%) was fabricated, and a 60% fiber loading showed the best mechanical properties. 0 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 447-453, 2009