To improve the interfacial adhesion of bamboo powder/plastic composites by using natural coupling agents, bamboo fibers (BFs) coated with urushiol-ferric (BCFeU) were obtained via in situ polymerization and BCFeU/ polypropylene (PP) composites were prepared. Direct correlations were found between coating ratio of BCFeU and activation time, concentration of urushiol, reaction time and concentration of ferric chloride. Five methods consisting of polarizing microscope, scanning electron microscope, X-ray photoelectron spectroscope, thermo gravimetric analysis, and differential scanning calorimetry were used to characterize the BCFeU. The results show that BCFeU was obtained successfully. Urushiol-ferric compounds were coated on the BFs by hydrogen bonding. Tensile test results and scanning electron microscope analysis of tensile fracture surfaces showed that urushiol-ferric acted as a coupling agent in BCFeU/PP composite. This results in 56% increase in elongation at break and 46% increase in maximum deflection of BCFeU/PP composite (compared with that of BF/PP composite) while there was no evident of variation in tensile strength and bending strength. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012