In this report we investigate and compare the characteristics of the cooperative-assembly of double-stranded DNA and random coil poly(styrene sulfonate) mixed with didodecyldimethylammonium bromide (DDAB). Film formation is attributed primarily to electrostatic interactions between anionic phosphate or sulfonate groups (DNA or PSS) and cationic ammonium groups of DDAB. It appears that the elasticity and morphology of such films are dependent on the length and the structure of polymers. Ethidium bromide (a nucleic acid stain and intercalating agent) was employed to probe the structure of polymers based on the photoluminescence response of this dye.