Hydroisomerization of n-hexadecane was investigated over the bifunctional catalysts Pt/ZSM-23, as a model reaction for n-paraffin dewaxing. Effort has been made to improve the selectivity to iso-hexadecane by introducing the magnesium promoter. The catalytic performances between Pt/ZSM-23 and magnesium promoted Pt/ZSM-23 were compared in terms of the correlation between conversion and selectivity. Magnesium promoter resulted in the changes of acidity and the dispersion of Pt metal; the acid amount decreased, and the Lewis acid sites increased. The dispersion of Pt metal was also improved. Magnesium-promoted Pt/ZSM-23 showed a higher yield of iso-hexadcanes due to its Lewis type acidic properties and higher Pt dispersion.