The blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) were obtained by melt blending at 310 degreesC for 2 min and quenching into an ice water. Mechanical properties and structural formation of unoriented amorphous PEN/PET blend films during drawing at 85,100 and 130 degreesC were studied by tensile tests and in situ X-ray measurements. The results obtained were compared with the pure PEN and PET. The PET film could not be drawn due to partial melt at above 100 degreesC and a lower drawing rate but the film blended with PEN was possible to be drawn. The crystallization of PEN/PET blend during drawing proceeded gradually due to the effect of PET at 100 degreesC though the crystalline reflections in the crystallization of pure PEN appeared suddenly by necking. This was evidenced by the formation of ex-form crystalline reflections of PEN as detected by in situ X-ray measurements.