We have studied nanorheological properties (viscosity and shear moduli) of aqueous xanthan solutions, in the oscillation frequency range up to 10 kHz by using magnetic particles that undergo Brownian relaxation and frequency dependent AC susceptibility (ACS). We used two magnetic nanoparticle (MNP) systems with different mean particle sizes of 80 nm and 100 nm. The determined viscosity and shear modulus of the diluted xanthan solutions from the ACS measurement of the two particle systems agree with traditional oscillatory rheological measurements. However, there is a particle size dependency that could be explained by comparing particles sizes with the xanthan microstructure