Herein, we describe the synthesis and characterization of two novel nickel complexes, [Ni(L-1)(2)] (1) and [Ni(L-2)(2) (CH3COO)]center dot 9H(2)O(CH3COOH) (2), containing (E)-2-(((2-(diethylamino)ethyl)imino)methyl)-6-ethoxyphenol (HL1) and (E)-2-(((2-(dimethylamino)ethyl)imino)methyl)-6-methoxyphenol (HL2) ligands. Complexes have been synthesized under conventional methods and characterized by elemental analysis, FT-IR, ICP-OES, TGA, and single crystal X-ray diffraction analysis. The geometry of the 2 is also supported by magnetic susceptibility and Q-TOF LC/MS analysis. The nickel ions are in square planar and distorted octahedral coordination environments, respectively. Complex 1 and 2 crystallizes in the monoclinic C1 c1 and C1 2/c1 space group. The antitumor activities of complexes 1-2 have been investigated. Both of the complexes showed dose dependent cytotoxicity and killed the newly established lung cancer cells via apoptotic pathway. The novel nickel complexes were determined as potential antitumor agents.