Blend films of poly(butylene succinate) (PBS) with cellulose triacetate (CTA) were prepared using a solvent-cast technique. The environmental stress cracking (ESC) behavior of commercial PBS films and that of as prepared PBS/CTA blend films were investigated in an aqueous NaOH solution. It was found that the fracture behavior of PBS films can be analyzed by linear fracture mechanics, that is, the stress-intensity factor, K, is found to control the crack-growth rate, da/dt, in PBS films. The enhancement of da/dt induced by increasing the normality of NaOH(aq) is more marked at a high value of K rather than at a low value of K. Furthermore, the ESC behavior of the PBS/CTA blends was studied in NaOH(aq). It was found that the behavior cannot be analyzed by linear fracture mechanics and that the addition of CTA into PBS increases the ESC resistance of the blends. Large-scale yielding of the material around the crack tip seems to be responsible for the high ESC resistance of the blends.