Miscibility in a series of blends, derived from Polyamide 11 (PA 11) and sulfonated polysulfone (SPSF) with different sulfonation degrees, 20, 44 and 70% has been investigated using differential scanning calorimetry, dynamic mechanical analysis, Fourier transform infra-red (FTIR) and Raman spectroscopy. The PA 11/SPSF(Na)(x) blends were prepared by solution casting from dimethyl formamide (DMF). Differential scanning calorimetry has shown a melting point depression of the equilibrium melting point of PA 11. From the melting point data of the blends of PA 11 with the SPSF with a 70% degree of sulfonation, the value of the polymer-polymer interaction parameter chi(12) was found to be -1.1 at elevated temperatures where it was determined. Less negative values were obtained for the blends of SPSFs with lower degrees of sulfonation, indicating the role of the sodium sulfonate group to the observed miscibility. Dynamical mechanical analysis revealed a non single-phase system at lower temperatures, although the T-g of PA 11 phase is shifted to higher temperatures. FT-IR and FT-Raman spectroscopic techniques have been used to confirm the nature of the specific interactions involved.