Arthrocereus spinosissimus is a species of cactus in the subfamily Cactoideae from Brazil.

[1][2] Arthrocereus spinosissimus grows upright with basally branching shoots.

Numerous, thin, yellowish thorns emerge from the closely spaced areoles.

[3] Arthrocereus spinosissimus is restricted to the Chapada dos Guimarães National Park in the Brazilian state of Mato Grosso at altitudes of 800 to 900 meters.

[4] The specific epithet spinosissimus is derived from the superlative of the Latin adjective spinosus for 'thorny'.