A cold area determining method, a memory controlling circuit unit, and a memory storage device are provided. The method includes: recording a plurality of logical update counts respectively corresponding to a plurality of logical units; calculating a plurality of reference update counts respectively corresponding to the plurality of physical erasing units according to the plurality of logical update counts; calculating a reference value according to a plurality of first logical update counts respectively corresponding to a plurality of first logical units; and determining at least one first physical erasing unit belonging to a cold area among the plurality of physical erasing units according to the reference value and the plurality of reference update counts.