The measurement of the internal conversion coefficient of 280keV γ – ray in 203HG have been investigated by means of calibrated 2ʺ x 2ʺ NaI(Tl)(scintillation detector which is sodium iodide activated with small amount of thallium) γ – rays spectrometer, using the standard γ – rays sources Co67 and Ba133 as shown in Table(1), and prepared a source of Hg203 from Hg203Cl2. It have been used some heavy element Au198 isotope Ti81[3, 6, 9, 12,13, 15]. The total internal conversion coefficient of a γ – ray may be calculated by taking the ratio of the number of detected X – ray to the γ – ray, Equation (14). In this workit have been discussed some important γ – ray interaction processes like photoelectric effect, Compton scattering and pair production etc. through which gamma ray interact with matter and get absorbed in it[1,2,16]. The measured value of internal conversion coefficient of 280KeV γ – ray in Hg203 at various source detector distances in centimeters (0.0, 3.2, and 4.2) which gives internal conversion coefficient (α) 0.230, 0.179 and 0.187 respectively. The average internal conversion coefficient α, of 280 keV γ – ray in Hg203is 0.2. By comparingthe measurement results with the standard value, it had been found that the measured values of internal coefficient of 280 KeVγ – ray in 203Hg was independent of source detector distance which was obvious and came out to be 0.20. Our experiment finding was in good agreement with the earlier reported value as 0.20.