An inner sole assembly for slippers or sandals includes a slipper or sandal made up of a sole, a retaining strap, a coupling pad, and an insole wherein the sole has a plurality of assembly holes properly preset at the top surface thereon for the retaining strap led through the insole and the coupling pad thereof respectively to be fixedly engaged therewith, and the coupling pad, better made of EVA or PVC foaming material, is sandwiched between the insole and the top surface of the sole to integrally combine the insole and the sole into one piece. The insole has a plurality of resilient supporting rings with air vents densely and neatly arranged in upright circular shapes at the upper surface thereon, an engaging underside formed at the bottom surface thereof to be fixedly attached to the coupling pad thereby, and a plurality of dividing passages defined at the adjacent sides of the closely juxtaposed resilient supporting rings thereof. Thus, in case tiny grains of sands/stones get caught inside the insole thereof, the sands/stones can be precisely flushed or knocked out there-from via the air vents of the resilient supporting rings in an easy and fast manner, achieving superior effect of massage as well as sand-draining and air-venting capabilities. Besides, the insole can also have bamboo charcoal contained therein to provide deodorization and anti-bacteria effects thereof.