The bay-ringed tyrannulet (Phylloscartes sylviolus) is a species of bird in the family Tyrannidae, the tyrant flycatchers.

Both sexes have a bright white iris, a pointed black bill, and bluish gray to slate legs and feet.

[5][6][7] The bay-ringed tyrannulet is found in southeastern Brazil from southern Minas Gerais and Espírito Santo south to Santa Catarina and west into eastern Paraguay and northeastern Argentina's Misiones Province.

It typically perches horizontally on a branch, usually with its tail cocked up, and makes short sallies to snatch or hover-glean prey from leaves and twigs.

It typically forages singly or in pairs and occasionally in small family groups, and often as part of a mixed-species feeding flock.

Both parents build the nest, a bag made mostly of moss with a side entrance hanging from a horizontal branch, typically between 10 and 25 m (35 and 80 ft) above the ground.

The bay-ringed tyrannulet's song is a "rapid, almost level twittering, sounding (simplified) like twitwi--twididirit-tjutju".