This work is a trial to reach the optimum composition and structure of cast iron used for anode fixation in the aluminum electrolytic cells. Grey iron with low- and high-phosphorus contents, spheroidal graphite irons with compositions typical of ferritic and pearlitic grades as well as grey iron with different carbon equivalent values were compared. A bench-scale experimental set up was used to simulate the operating conditions at the steel stub/cast iron collar/carbon anode connection. The change in microstructure and electrical resistance was measured at temperatures up to 850°C for 30 days, which correspond to the electrolytic cell operating conditions. The thermal expansion properties of irons were measured using a high precision automatic dilatometer. The electrical resistance at the connection was found to decrease with spheroidal graphite irons. In flake graphite irons the resistance decreases with lower phosphorus content as well as higher CE values due to the enhanced graphitization potential during solidification, which increases the contact pressure at the connection. Decomposition of ledeburitic carbides in the structure plays – to lower extent – some role in increasing the contact pressure. This contact pressure rather than the resistivity of the cast iron seems to play the dominant role in determining the electrical resistance of the connection.