Love wave acoustic sensors have shown through the years a great potentiality regarding measurements in liquid environments, especially in the field of biosensors. Their high sensitivity to surface perturbations make them also good candidates for micro-rheology. In this paper, we demonstrate that a Love wave sensor response is also very sensitive to the molecular structure of polymers by investigating its behavior to aqueous poly(ethylene glycol) solutions of various molecular weights. We also report the ability of this type of sensor to determine the critical molecular weight between entanglements (Mc).