Earlier, poly(epsilon-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) were found to be miscible on molecular level at 8 up to 28 wt.% of acrylonitrile (AN) in SAN copolymer [1]. The combination of PCL and different copolymers of SAN thus offers an opportunity to investigate the effect of`miscibility on some key properties of the blends, e.g. rheological or mechanical. In this paper blends containing SAN with 25 wt.% of AN (miscible SAN-25) and 35 wt.% of AN (immiscible SAN-35) were used for this purpose. Blends of PCL with various contents of SANs up to 40 wt.% were prepared by melt mixing in a Brabender laboratory mixer. The miscibility of the mixed PCL/SAN blends was investigated by differential scanning calorimetry (DSC). The blends rheological characteristics were determined on a Rheoflixer capillary rheometer at various temperatures. Rabinowitsch and Bagley corrections and the power-law relation were used. The extrudates were observed under a scanning electron microscope. In addition, mechanical testing was performed on a tensile testing machine. It was found that blends of PCL with a minor amount of miscible SAN-25 provide a better balance of rheological and mechanical properties than those of pure PCL. The immiscible blend shows properties inferior to the miscible one. Immiscible SAN-35 increases viscosity, shear thinning and extrudate swell of PCL more than the miscible type. In contrast to the miscible blends containing SAN-25, which were without any form of unstable flow at shear rates of 10 to 10 000 s(-1), melt fracture occurs in the immiscible blends with SAN-35. Positive synergism in tensile strength and elongation at break can be seen for 90/10 PCL/SAN-25 blend processed at 130 degrees C. The addition up to 30 wt.% of SAN-25 miscible with PCL increases elongation at break.