The metal atom net charge correlation (MANCC) was successfully used to study the relative catalytic activities of 20 bis(imino)pyridyl Fe(II) and bis(imino)pyrimidyl Fe(II) complexes for olefins polymerization/oligomerization through modifying the Dreiding force. The net charge range on the central metal Fe was found 0.6295-0.8310, which was considered in the present study as two areas, e.g. the lower charge area (0.6295-0.7000) and the higher charge area (0.7000-0.8310). The observations reveal that the catalytic activity of bis(imino)pyridyl Fe(II) and bis(imino)pyrimidyl Fe(II) complexes does not monotonously vary with the net charge on the central metal as we found for other metal system before. There possibly is an interesting turning point around 0.7000. The activity increases with the net charge in the lower charge area, while the catalytic activity increases with reducing the net charge in the higher area. The reason that the Fe(II) catalysts possess such properties was discussed. (C) 2004 Elsevier B.V. All rights reserved.