We present a quantitative structureeactivity relationship study performed over a set of bis(imino)pyridine iron catalyst used for olefin po-lymerisation. The experimental results were previously obtained by our research group. The structural variability of this catalyst set is mainly focused on the substituents of the aryl rings. We managed to find a statistically robust model which correlates the experimentally determined polymer's molecular weight with the steric and electrostatic fields. As a result the main contribution comes from the steric contribution which amounts up to 75% of the model. The predictive capability of the model was successfully probed with a test set of catalyst reported in the literature by other research group.