Small angle X-ray scattering (SAXS) is familiar to the polymer community as a method for structural analysis. Here we applied the SAXS experimental technique to obtain the macromolecular parameters ( radius of gyration Rg, radius R, Specific surface area Ss and surface fractal dimension Ds) of two different polythiophene derivatives Poly (3-Octylthiophene) (POTH) and Poly (3,3â -dioctyl-2,2â , 5'2â -terthiophene) (POTTOT) thin films. Thin films of these two polymers were prepared on a 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 Guinier approximation the radius of gyration of POTH and POTTOT particles are determined as 10.73 à and 9.99à respectively. Porod approximation is used to find specific surface area of POTH and POTTOT polymeric thin films and they are determined as 3.6X10⁸ cm^-1 and 3.00à 10⁸ cm^-1 respectively. The surface fractal dimension of POTH and POTTOT thin films are calculated as 2.85 and 2.65 respectively.