Samples of multiblock poly(ether-ester) copolymer doped with magnetic γFe2O3 nanoparticles (at small concentrations of 0.1 wt. % and 0.3 wt. %) have been investigated by DSC method to study the melting and crystallization behavior. Two forms of magnetic γFe2O 3 nanoparticle filler were used: solid-state grains and a suspension of γFe2O3 with palmitic acid in toluene. Application of the solid filler caused formation of agglomerates of size of about 20 μm while in the suspension form separate nanoparticles were in the range 10-20 run. The thermal and thermo-oxidative stability of composites was analyzed by conventional TGA analysis. The DSC results showed that crystallization and, to a smaller extent, melting, were considerably affected by the introduction of magnetic nanoparticles. The main influence is a shift in the crystallisation temperature up to 20 °C and melting/glass transition shift up to 6 °C. Thermogravimetric analysis showed significant enhancement of thermal and thermo-oxidative stability of the composites with respect to pure PEE. The dependence of thermal parameters on the concentration of magnetic filler has shown that the largest agglomerates produced the biggest change in all thermal parameters