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Coloration is grayish or grayish brown above and white below.
Beamys is distinguished externally by the naked, white-tipped tail of medium length. The underside of the tail is dark on the proximal quarter and whitish for the rest of its length. The tail is flattened, with sharp edges, and the lower side is wider than the upper, so that in cross section its shape resembles that of a truncated pyramid. The tail is not noticeably scaly, but only the basal centimeter is hairy. Like the other two genera of the subfamily Cricetomyinae, Cricetomys and Saccostomus, Beamys has cheek pouches.