Microstructure, martensitic transformation behavior and magnetic properties of Ni44−xFexCo6Mn39Sn11 (x=0, 1, 2at.%) melt spun ribbons have been investigated. The influence of iron addition has been thoroughly studied by means of electron microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that addition of 1at.% of iron into quaternary Ni–Co–Mn–Sn Heusler alloy drastically decreases the martensitic transformation temperature by more than 100K. Higher concentration of iron leads to complete suppression of martensitic transition. The structure of samples change from fully martensite (12M) through mixed austenite-martensite (L21+10M) to fully austenite (L21) with increase of iron content. Addition of 1at.% of iron leads to enhance magnetization of both austenitic and martensitic phases and also a small increase of Curie temperature occurs. The largest change of magnetic entropy under 15kOe measured 2.9 and 0.65Jkg−1K−1 for alloys where x=0 and 1, respectively.