In this article, the relationship between fracture surface feature and impact properties of poly(butylene terephthalate) (PBT) was investigated. The results indicated that the fracture surface morphology of notched impact specimens tested in the temperature range from 196 to 180 A degrees C could be differentiated into brittle (T a parts per thousand currency sign 20 A degrees C) and ductile appearances (T > 20 A degrees C). The fracture surface roughness was characterized by surface roughness ratio (R (s)) and fractal dimension (D (b)). The fracture mode significantly influenced the relationship between impact strength and fracture surface roughness. When PBT fractured in a brittle mode, both the measured values of R (s) and D (b) could correspond to impact strength appropriately. On the contrary, when PBT fractured in a ductile mode, their relationship became not statistically significant because the area of the plastic deformation zone instead of fracture surface roughness might be the major factor influencing impact strength.