Small angle X-ray scattering (SAXS) experimental technique is applied in obtaining the macromolecular parameters (radius of gyration Rg, radius R, specific surface area Ss and surface morphology) of two polythiophene derivative (poly-(3′-octyl-2, 2′-terthiophene) (POTT) and poly-(3-octyl-2,2′; 5′2″-terthiophene) (POTT)) thin films. Nanosized thin films of these two polymers were prepared on glass substrate with thickness around 3.5 μm by spin coating. SAXS experiments are performed with an 18-kW rotating anode X-ray generator equipped with a Cu target. A two-dimensional proportional counter is employed to detect the scattered X-rays intensity. Analysis of SAXS data using the Guinier approximation, the radius of gyration of POTT and PTOTT particles are determined as 10.28 and 11.05 Å, respectively. Similarly, the radii of these samples are determined as 13.28 and 14.14 Å. Porod approximation is used to find specific surface area of POTT and PTOTT nanostructured polymeric thin films, and they are determined as 4.78×108 and 5.38×108 cm-1, respectively. The surface fractal dimensions of POTT and PTOTT films are determined as 2.81 and 2.65, respectively.