In this paper we investigate the third-order nonlinear optical properties of spin deposited thin films of DNA-based complexes using the optical third harmonic generation (THG) technique at a fundamental wavelength of 1064 nm. We found that the third-order susceptibility, X-(3)(-3 omega;omega,omega,omega), of DNA-based films was about one order of magnitude larger than that of our reference, a pure silica slab. in thin films doped with 5% of the chromophore disperse red 1 (DR1), a two order of magnitude larger value of X-(3)(- 3 omega;omega,omega,omega) was observed. (c) 2007 Elsevier B.V. All rights reserved.