Depolymerization of aqueous guar gum using hydrodynamic cavitation has been investigated for the first time, with a detailed understanding into the effect of initial concentration of polymer, inlet pressure, geometry of cavitating device, operating temperature and addition of potassium persulfate (KPS). The extent of depolymerization has been analyzed in terms of reduction in intrinsic viscosity using Ubbelohde glass capillary viscometer. It has been observed that lower initial concentration, higher inlet pressure, slit venturi as cavitating device and addition of KPS result in higher extent of depolymerization. Use of hydrodynamic cavitation alone under optimized conditions resulted in about 70% reduction in intrinsic viscosity whereas addition of KPS under optimum loading enhanced the extent of reduction to 96%. Kinetic analysis established that the kinetic rate constant increased with an increase in the temperature and concentration of KPS. FTIR analysis demonstrated that there were no structural changes and the chemical identity was retained. Hydrodynamic cavitation has been demonstrated to be more energy efficient and applicable at larger scale of operation as compared to ultrasound based operation. (C) 2015 Elsevier B.V. All rights reserved.