This paper reports on the interpolymer complex formation and polymer blends between poly(monomethyl itaconate) (PMMI) and two polymer accepters poly(N,N-dimethylacrylamide) (PDMA) and poly(ethyloxazoline) (PEOX). We have found that the formation or inhibition of interpolymer complexes for these systems strongly depends upon the solvent medium. The stoichiometry of the complexes prepared from methanol solutions has been calculated from elemental analysis, resulting in a stoichiometry near a 1:1 ratio. Specific interactions of PMMI/PDMA and PMMI/PEOX complexes and blends have been characterized by FTIR. Strong hydrogen bonding for complexes and blends has been found. Finally, a calorimetric and thermogravimetric study of the complexes and blends has been performed in a wide temperature range.