The effect of magnesium addition on the catalytic properties of PtSnK/γ-Al 2 O 3 catalyst for isobutane dehydrogenation has been investigated by reaction tests and some physicochemical characterizations such as nitrogen adsorption, TEM, H 2 chemisorption, TPR, H 2 -TPD, and TPO. It was found that with the suitable addition of magnesium (0.2 and 0.4wt.%), the platinum dispersion increased, while the carbon depositions decreased. The presence of Mg in the PtSnMgK/γ-Al 2 O 3 catalysts could not only strengthen the Sn–Al 2 O 3 interaction, but also stabilize the oxidation states of Sn species, which resulted in the increased reaction activity and stability. However, when the content of magnesium was excessive (0.6 and 0.8wt.%), the character of platinum and the interfacial properties between the metal and the support changed evidently, which was disadvantageous to the reaction. In our experiments, addition of 0.4wt.% Mg to PtSnK/Al 2 O 3 catalyst showed the best catalytic performance. After reaction for 6h, selectivity toward isobutene of higher than 94% was achieved with the corresponding conversion value of about 29.0%.