In order to study the thermal shrinkage behavior, the blend yarns were made from two types of filaments with different shrinkage properties. The different filaments were obtained by different spinning conditions (melt spinning temp.: 295 $^{circ}C$, draw ratio : 2.60, 2.85, 2.90, draw temp.: 25 $^{circ}C$, 100 $^{circ}C$, 130 $^{circ}C$). The values of shrinkage, thermal stress and mechanical properties of the blend yarns and constituent filaments were investigated. The best spinning condition (draw ratio 2.95, draw temp. 100 $^{circ}C$) was determined from the above results, and the blend yarn was made by interlacing. Using these interlaced yarn, multi-step shrinkage test was carried out. The trend of shrinkage of interlaced yarns had a good agreement with that of thermal stress measurements. Total shrinkage of the interlaced yarn was found to be between the value of the highly shrinkable yarn and that of the regular yarn. The final tenacity and initial modulus of interlaced yarn depended on the values of the regular and the highly shrinkable yarns respectively, and the elongation was independent of the those of the constituent yarns.