The effect of iron on the glass transition, the viscosity of the supercooled liquid and the crystallization behaviour of (Zr_0.650Al_0.075Cu_0.175Ni_0.100)_100−xFe_x and (Zr_0.55Al_0.10Cu_0.30Ni_0.05)_100−xFe_x metallic glasses (0≤x≤15) was investigated using parallel plate rheometry, differential scanning calorimetry and X-ray diffraction. Iron additions shift the glass transition as well as the crystallization to higher temperatures, and increase the viscosity of the supercooled liquid. Increasing iron content reduces the extension of the supercooled liquid region. This mainly results from a stronger composition dependence of the glass transition than the crystallization temperature. The results are discussed with respect to the kinetics and thermodynamics of the supercooled liquid suggesting that changes in the atomic arrangement and in the free volume are the microscopic origin for the differences in the viscosity and the thermal stability of the alloys. All investigated alloys are rather strong glasses as expressed by a relatively high melt viscosity, a low Vogel-Fulcher Tammann (VFT) temperature and a rather high fragility parameter, but in general (Zr_0.55Al_0.10Cu_0.30Ni_0.05)_100−xFe_x alloys are slightly stronger glasses than (Zr_0.650Al_0.075Cu_0.175Ni_0.100)_100−xFe_x alloys.