In this article, the miscibility of poly(epsilon-caprolactone) (PCL) with poly(styrene-co-acrylonitrile) (SAN) containing 25 wt % of acrylonitrile is studied from both a qualitative and a quantitative point of view. The evidences coming from thermal analysis (differential scanning calorimetry) demonstrate that PCL and SAN are miscible in the whole range of composition. The Flory interaction parameter chi(1,2) was calculated by the Patterson approximation and the melting point depression of the crystalline phase in the blends; in both cases, negative values of chi(1,2) were found, confirming that the system is miscible. The interaction parameter evaluated within the framework of the mean field theory demonstrates that the miscibility of PCL/SAN blends is due to the repulsive interaction between the styrene and acrylonitrile segments in SAN. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2129-2139, 2010