Rhenium was determined in representative molybdenite samples (concentrates) from the Aksug, Erdenetuin-Obo, Zhireken, Shakhtama and Sora porphyry Cu–Mo and Mo–Cu deposits of Russia (Siberia) and Mongolia. The Re contents in the majority of the concentrates are low, ranging from 6 to 460 ppm. The maximum Re contents were determined in molybdenite concentrates from the Aksug (460 ppm Re) and Erdenetuin-Obo (199 ppm Re) Co–Mo porphyry deposits and are significantly higher than those from the Zhireken, Shakhtama and Sora Mo–Cu porphyry deposits. The Re content of molybdenite concentrates from the studied Mo–Cu porphyry deposits (6 to 57 ppm) are, however, comparable to those from comparable deposits worldwide. The Aksug and Erdenetuin-Obo deposits, with relatively elevated Re content, differ from the Zhireken, Shakhtama and Sora deposits with lower Re contents in terms of (1) higher Cu/Mo ratio; (2) lower δ³⁴S and ⁸⁷Sr/⁸⁶Sr values; (3) silica and alkali contents of the host rocks; (4) the alteration type of the associated rocks; (5) the elevated Cl activity in the fluid; (6) the lower temperature of the molybdenite formation; and (7) the higher oxidized conditions. The Re contents of molybdenite from porphyry Cu–Mo deposits may therefore be related to the composition of parent magmas themselves and/or fractionation, sources of the material, and variations of physical and chemical conditions of crystallization (fO₂, Cl activity, P, T).