The present invention relates to a method for producing anhydrous galactose derived from seaweed, and provides an improved production yield of 3,6-anhydro-L-galactose (AHG) from agarose or agar through multiple steps involving acid hydrolysis of agar or agarose for producing agarobiose, neutralization of the acid hydrolysate, and purification of AHG using a microorganism metabolizing galactose after enzymatic hydrolysis of agarobiose.