New two lanthanide complexes of Neodymium (III) and Gadolinium (III) ions were prepared based on 2‐Cyano‐N′‐([4‐oxo‐4H‐chromen‐3‐yl]methylene) acetohydrazide as a chelating agent. The prepared Nd(III) and Gd(III) complexes were characterized via elemental analysis, molecular conductance, IR, and TGA. The obtained results showed the chelating agent behaves as tridentate via oxygen of γ pyrone and carbonyl groups and nitrogen of the azomethine group. The antitumor activity of isolated complexes was investigated against the Ehrlich Ascites Carcinoma cell line (E.A.C). The results of antitumor activity cleared that Gd(III) complex has higher activity than Nd(III) complex and moderate activity relative to cisplatin and 5‐Furacil. Besides, DFT calculations were estimated for prepared Nd(III) and Gd(III) complexes by the Gaussian program. Theoretical parameters were calculated. The energy gap values confirmed the higher activity of the Gd(III) complex over the other Nd(III) complex. In addition, the composite films of Nd(III) and Gd(III) complexes were prepared using the cast technique. The electrical and optical absorption properties of these polymer composites were analyzed.