The present study investigated fracture and various mechanical properties of polyoxymethylene (POM) hybrids in tension and in flexure. The hybrids examined consisted of short glass fibers (GF) and spherical glass beads (GB). Comparisons are made between experimentally observed values and predictions based on the rule-of-hybrid mixtures for hybrid strength, modulus, Impact strength, fracture tough ness, and strain energy release rates. Results indicated that tensile strength, flexural modulus, and fracture toughness of POM/GB/GF hybrid composites can be estimated from the following rule-of-hybrid mixtures P-H = P-POM/GF chi POM/GF + P-POM/GB chi POM/GB where P-POM/GB and P-POM/GF are the measured properties of the POM/GB and POM/GF composites, and chi(POM/GB) and chi(POM/GF) are the hybrid ratio (by volume) of the glass bead and that of glass fiber, respectively. In view of this, none of the aforementioned properties show any signs of a hybrid effect. Flexural strengths, impact strengths, and strain energy release rate ail showed the existence of a negative hybrid effect where negative deviation from the rule-of-mixtures behavior was observed. The latter was closer to the estimation based on the inverse rule-of mixtures.