A rapid one-pot method for hydrolysis of sodium alginate for determining M/G ratio has been developed under mild conditions, using microwave irradiation. Poly-mannuronic acid (PMA) and poly-guluronic acid (PGA) ratio was determined (M/G 0.38), which was similar to that (M/G 0.39) obtained by the conventional method, using sodium alginate of Sigma as reference sample for bench marking. For validation of the method PMA and PGA were characterized by density, porosity, viscosity, optical rotation measurements, ¹³C NMR, FT-IR, thermogravimetric analysis (TGA), X-ray diffraction, circular dichroism (CD), molar mass distribution (GPC) and scanning electron microscopy (SEM).