To provide a defect inspection method and a defect inspection device of a sealed honeycomb structure, capable of specifying the position of a cell having a defect and of readily grasping the defect size.

In this method for inspecting a penetration defect of a sealed honeycomb structure 1 equipped with a honeycomb structure 2, wherein a plurality of cells 9 communicated between two end faces are partitioned and formed by a porous bulkhead 7, and a sealing part 11 disposed so as to seal either of two opening ends of each cell 9, particles 51 for quantification having a prescribed particle size range are introduced into the cell 9 from either end face; the number and the particle size of the particles 51 for quantification passing a penetration defect 17 and discharged from the end face on the opposite side are measured relative to each cell having the defect through which the particles are discharged; and the defect size is quantified from the measured number and particle size of the particles 51 for quantification.