The effective atomic number (Z(eff)) of composite materials has been determined by measuring the backscattered gamma photons at 180 degrees. A 661.6 keV gamma photons from Cs-137 radioactive source are allowed to scatter at an angle of 180 degrees from the sample. The backscattered photons at 180 degrees from the sample are detected with "2 * 2" NaI(Tl) scintillation gamma ray spectrometer coupled to 16 K Multi Channel Analyzer (MCA). It is observed experimentally that the intensity of backscattered photons increases initially with increasing the thickness of the target and then it becomes saturated above a certain thickness. By knowing the saturated thickness values for known atomic number of the elemental targets, the Z(eff) of composite materials has been determined. The experimentally measured Z(eff) values have been compared with theoretical values predicted by direct method, power law method and AutoZ(eff) code. (C) 2018 Published by Elsevier B. V.