Aphonopelma marxi is a species of spider in the family Theraphosidae (tarantulas), found in United States (Arizona, New Mexico, Colorado and Utah).

[1][2] Aphonopelma marxi is generally dark brown to black in color, very hairy, with some orange to red hairs on the abdomen.

[3] A. marxi can be distinguished from other species of the genus living in the same places by its dark color, overall hairy appearance, size and habitat.

[3][2] Smith also recognized two species, A. behlei and A. vogelae, that in analyses performed by Hamilton et al. in 2016 were not distinguished from A. marxi on either morphological or molecular grounds, and so were treated as junior synonyms.

[2] Aphonopelma marxi is widely distributed in areas of higher elevation in the "Four Corners" region of northern Arizona, northwestern New Mexico, southwestern Colorado, and southeastern Utah.