Abstract Objective- A suitable analytical method is applied for studying the crystallinity, crystallite size and inter-planer distance in order to investigate compatibility of polymers. Approach- X-ray diffraction and scanning electron microscopy (SEM) were carried out for thin films of guargum (GG) - a natural polymer, polyacrylonitrile (PAN) - a synthetic polymer, GG grafted with PAN (GG-g-PAN), and a layered composite of GG and PAN (GG/PAN). Findings- It explains the relation between crystallinity and mechanical strength of composite polymers. SEM result approves better compatibility in GG-g-PAN in comparison with GG/PAN. The composite, GG-g-PAN has been observed to have better crystallinity, mechanical strength and morphology than GG/PAN. Limitations-X-ray diffraction patterns is an approximate method to calculate about crystallinity of thin films. Practical implication-The present work will give insight into application of these films. Originality-The present work is carried out by author to characterized thin films of polymers & their composites prepared in her earlier publications. Keywords: Guargam, polyacryloritrile, polymer composite, XRD, SEM.