Xylophanes mulleri is a moth of the family Sphingidae. It is known from Mexico.
The length of the forewings is about 33 mm. The forewing upperside is uniform brown and separated from a well-developed brown fourth postmedian line by a strongly contrasting pale yellow line running from the inner margin to the apex. The fifth postmedian line and two submarginal lines are brown and conspicuous against a paler brown ground.
Adults are probably on wing year-round.
The larvae probably feed on Rubiaceae and Malvaceae species.