A series of chromium(III) complexes ligated by tridentate ligands of 2-imino-1,10-phenanthrolines, LCrCl3 (L=2-(2,6-(R1)2C6H3N=CR)-1,10-phen) was synthesized and characterized by elemental and spectroscopic analyses as well as single-crystal X-ray crystallography. X-ray crystallographic analysis of 2 (R=Ph, R1=Et), 4 (R=Me, R1=Me) and 12 (R=H, R1=i-Pr) reveals that the geometry around the chromium atom is octahedral. Upon activation with MAO, these complexes exhibited high activities for ethylene oligomerization (up to 1.15×107gmol−1(Cr)h−1) and moderate activities for ethylene polymerization. The oligomers and polymers obtained were α-olefins, and the distribution of oligomers resembled the Schultz–Flory rule. Various reaction parameters were investigated in detail, and the results revealed that both the steric and electric effects of ligands affected the catalytic activities of their chromium complexes as well as the distribution of the products.