Oryzomys nelsoni, also known as the Nelson’s Rice Rat, is an extinct rodent of María Madre Island, Nayarit, Mexico.

Since its first description in 1898, most authors have regarded it as a distinct species, but it has also been classified as a mere subspecies of the marsh rice rat (O. palustris).

[7] Clinton Hart Merriam identified the mammals they obtained, including four specimens of Oryzomys nelsoni, which were deposited in the United States National Museum and remain there.

In 2009, Michael Carleton and Joaquin Arroyo-Cabrales revised the Oryzomys of western Mexico and confirmed that O. nelsoni is a very distinct species.

[14] Many aspects of the systematics of the O. couesi section remain unclear and it is likely that the current classification underestimates the true diversity of the group.

[5] The interparietal bone, part of the roof of the braincase, was broad and the incisive foramina, which perforated the palate between the incisors and the molars, were relatively short.

[30] Oryzomys nelsoni is thought to have fed on plant material such as weeds, fruit, and seeds, and more rarely on animals such as fish and invertebrates.