Abstract: Molecular sieves of SAPO-41 with different silicon contents were synthesized and characterized by XRD, N2 adsorption, XRF, pyridineIR and 29SiMAS-NMR. The isomerization properties of the SAPO-41 were investigated by using m-xylene as a feedstock. The SAPO-41 obtained from the synthesis gel with SiO2/Al2O3=0.3 showed the highest activity to the isomerization of m-xylene and the largest number of Brnsted acid sites was also observed with PyIR over this sample. The state of Si in the framework of SAPO-41 plays a predominant role on the Brnsted acidity. The relationship between the activity and the acidity obtained in this study can be explained in terms of the distribution of stronger Brnsted acid sites.