Chandless State Park, State park in Acre, Brazil

Chandless State Park covers 695,303 hectares across Sena Madureira, Santa Rosa do Purus and Manoel Urbano. The Chandless River enters from Peru and runs northeast to join the Purus, fed by the Cuchichá and Chandless-chá streams. Terrain is Amazon plain with flooded areas, oxbow lakes, 15-metre dry ravines, rocky outcrops, rapids and sandy beaches.

The area takes its name from a British explorer who conducted expeditions along river routes in the mid-1800s. This early exploration documented a region that would eventually become protected.

The park's name honours William Chandless, a British explorer who surveyed the Purus River in 1864–66 and received the Victoria Gold Medal; the river was formerly called Aracá. When the park was created in 2004, about 12 families (60 people) lived in the area and supported its protection. Parts of the park are used by uncontacted nomadic Mashco-Piro people.

The headquarters on the Chandless River can be reached by charter float plane from Rio Branco or by boat from Manoel Urbano: about 8 hours by speedboat in the rainy season, around 2 days by larger boat at any time. Rivers are fullest from October to May and lowest from June to September, when access is harder. The forest is hard to walk through because of thorny bamboos.

The park sits at the centre of the southwestern Amazon bamboo forest region and holds three bamboo species of the Guadua genus found nowhere else. A 2010 rapid ecological assessment recorded 264 plant species, 24 of them palms, and 407 bird species. At least 13 bird species are tied to the bamboo stands.