The purpose of this research is to study the effect of various applicator compositions on dosimetric parameters and dose distribution of (192)Ir, (137)Cs, and (60)Co sources, using Monte Carlo simulation techniques. To study the effect of applicators on source dosimetry, the dose rate constant, and radial dose function and isodose curves for the above noted sources were calculated in the presence and absence of plastic, titanium, and a stainless steel applicators. The effects of the applicators on the dosimetric parameters and isodose curves of these sources were dependent of the source type and materials of the applicator. The (192)Ir source with the stainless steel applicator has the maximum difference of dose rate (4.2 %) relative to the without applicator case. The (60)Co source with plastic applicator has the minimum dose variation. Moreover, this effect is higher for lower energy sources. Ignoring the effect of applicator composition and geometry on dose distribution may cause discrepancies in treatment planning. Plastic applicators have the least radiation attenuation compared to the other applicators, therefore, they are recommended for use in brachytherapy. A table of correction factors has been introduced for different sources and applicators with different materials for the clinical applications.