The black-capped gnatcatcher (Polioptila nigriceps) is a small songbird in the family Polioptilidae. It is found in Mexico and the United States.
The black-capped gnatcatcher is 10 to 12 cm long. Adults are blue-gray on the upperparts with white underparts. They have a long slender bill and a long black tail with mostly white outer feathers. Males in alternate (breeding) plumage have a glossy black cap. The female's gray upperparts have less of a bluish tint but are otherwise similar to the non-breeding male. This species is very similar to the black-tailed gnatcatcher (P. melanura).