The plain-breasted piculet (Picumnus castelnau) is a species of bird in subfamily Picumninae of the woodpecker family Picidae.

Their iris is brown, the beak black with a blue-gray base to the mandible, and the legs greenish yellow to bluish gray.

[4][5] The plain-breasted piculet forages for its diet of small insects on slender branches and stems, usually about 6 to 15 m (20 to 49 ft) above the ground but sometimes lower along forest edges.

The plain-breasted piculet's song is "a high-pitched, rapid, falling trill: tree'e'e'e'e'e'e."

[4] The IUCN has assessed the plain-breasted piculet as being of Least Concern, though its population size is unknown and believed to be decreasing.

[1] It is thought to be "fairly common", and "can occupy woody second growth...and so may be able to tolerate moderate levels of habitat disturbance.