Pelecyphora duncanii is a species of flowering plant in the family Cactaceae, native to the southern United States.

The circular, almost spherical to inverted conical green shoots reach heights of 2.5 to 6 centimeters and the same diameter.

[2] Pelecyphora duncanii is widespread in the United States in southern New Mexico and western Texas.

The specific epithet duncanii honors the American Frank Duncan, who owned the mining field where the species was discovered.

David Aquino & Daniel Sánchez moved the species to Pelecyphora based on phylogenetic studies in 2022.