The present invention relates to a method for measuring porosity of a rock according to the present invention including: (a) capturing a first image by using SEM with respect to a rock sample; (b) determining a first area of a portion determined to be a heavy mineral in the first image; (c) immersing the rock sample in an aqueous solution in which a gadolinium compound is dissolved in that the aqueous solution flows into pores and the gadolinium compound is deposited in pores inside the rock sample; (d) capturing a second image by using SEM with respect to the rock sample; and (e) determining a second area of a portion determined as a heavy mineral and a pore in the second image, and then subtracting the first area from the second area to determine an area of pores in the rock sample.