AbstractThe fracture behavior of biodegradable fiber–reinforced composites as a function of fiber content under different loading conditions was investigated. Composites with different fiber content, ranging from 5 to 20 wt%, were prepared using commercial starch‐based polymer and short sisal fibers. Quasistatic fracture studies as well as instrumented falling weight impact tests were performed on the composites and the plain matrix. Results showed a significant increase in the crack initiation resistance under quasistatic loading. This was caused by the incorporation of sisal fibers to the matrix and the development of failure mechanisms induced by the presence of the fibers. On the other hand, a modest increasing trend of the resistance to crack initiation with fiber loading was detected. An improved fracture behavior was also observed when the impact loading was parallel to the thickness direction. Under these experimental conditions, the composites exhibited higher values of ductility index, energy at initiation and total fracture energy than the plain matrix. Furthermore, an increasing trend of these parameters with fiber content was detected in the biocomposites. Overall, the addition of sisal fibers to the biodegradable matrix appears to be an efficient mean of improving fracture behavior under both quasistatic and impact loading conditions. POLYM. COMPOS. 26:316–323, 2005. © 2005 Society of Plastics Engineers