Solid films of deoxyribonucleic acid (DNA) from salmon testes were prepared by a solvent-casting method. The thermal molecular motion of the DNA film was examined by dynamic mechanical analysis (DMA). Four absorption peaks and one shoulder of the loss modulus were observed in the temperature domain from approximately 150 to 490 K. To assign these, thermal analysis employing thermogravimetry (TG) and differential thermal analysis (DTA) was used in conjunction with ultraviolet (UV)-visible and Fourier-transform infrared (FT-IR) spectroscopy. It seems most likely that, in order of increasing temperature, they are a B(I)→B(II) conformational transition, a relatively large-scale movement associated with water molecules, water evaporation, thermal denaturation of DNA, and a glass transition.