The Hupacasath are a Nuu-chah-nulth band in the Alberni Valley, Vancouver Island, BC. They formerly consisted of three Coast Salish groups which, reduced by disease and prolonged warfare in the historic period, amalgamated as one community. Their traditional territories included Alberni Inlet, the Somass River, Sproat Lake and Great Central Lake.

In the late prehistoric and early historic period, Nuu-chah-nulth groups invaded Alberni Inlet, pushing the Coast Salish groups into their Alberni Valley territories. Eventually the Hupacasath adopted the Nuu-chah-nulth language and culture, but retained their Salish orientation to river, lake and inland environments. Elk and deer were important for subsistence.

Today the Hupacasath live at Ahahswinis reserve, near Port Alberni.