Abstract: The minimal log discrepancy is an invariant of singularities related to termination of flips. The ACC for minimal log discrepancies is still unknown in dimension three, and it is one of the most important remaining problems in the minimal model theory of threefolds. In the talk, I will explain a proof of the ACC for minimal log discrepancies on smooth threefolds. More introductory exposition will be given in my seminar talk at Academy of Mathematics and Systems Science on the preceding day, 15 Oct.