Glenmacnass Waterfall (Irish: Gleann Log an Easa, "the glen of the hollow of the waterfall") is an 80-metre cascade located at the head of the Glenmacnass Valley in the Wicklow Mountains.

Fed by the Glenmacnass River, which rises on the southeast slopes of Mullaghcleevaun, the water reaches the lip of the falls at roughly 350 metres above sea level before dropping in three staggered stages to the valley floor.

Tonelagee mountain lies to the west and Scarr to the east. The waterfall is easily accessed via the R115, also known as the Military Road, which runs between Sally Gap to the north and the village of Laragh to the south.

It is a well-known scenic stop in the Wicklow Mountains and draws visitors year-round. Those viewing the falls are advised to remain on the road side of the boundary fence and not attempt to approach the top of the drop.