Butadiene polymerization using a series of PNP-pincer ligated iron(II) complexes 1-3 as a catalyst was investigated. To see electronic effects, complex 3, bearing electron-donating amino group on pyridine ring, was newly synthesized. All the complexes promoted butadiene polymerization at room temperature upon activation by methylaluminoxane (MAO) to give high molecular weight polymer. Polybutadiene obtained from complex 2 contained 76% cis-1,4 sequence, which is the same level as the previous highest results using iron catalysts. Electron-donating substituents on the ligand reduced the ratio of 1,4-sequence in the obtained polymer, whereas steric effects on phosphorous atoms raised cis-specificity.