A frequency-resolved thermal lensing (TL) approach to measure thermal diffusivity properties of both diluted liquid solutions and silver nanoparticle colloidal suspensions is demonstrated. The experiment is based on a classical two-color pump-probe TL configuration, which is adapted to measure the induced TL signal as a function of the chopping frequency of the pump beam. Because of the thermal diffusivity lengths in the samples, the TL signal decreases exponentially with the increment of the frequency. The exponential decay factor can be associated with the thermal diffusivity of the medium. Measurements are performed on diluted liquid solutions and silver nanoparticles suspended in a PVP solution. A suitable fitting to a theoretical model based on the Fresnel diffraction approximation of the experimental data is obtained. This work demonstrates the feasibility of using this approach for the thermal characterization of nanoparticles in liquid solutions. Thermal diffusivity as low as 0.094×10(-7) m2 s(-1) can be estimated by using this approach.