The Yellow-faced Grassquit (Tiaris olivaceus) is a passerine bird which breeds from central Mexico to Colombia and northwestern Venezuela, and also on the Greater Antilles. It is a vagrant to the United States and has been introduced to Hawai?i. It was formerly alled with the American sparrows and placed in the Emberizidae.

It is a small bird with a conical bill, sharper than that of the related seedeaters. It is 3.9-4.2 in (10-10.7 cm) long and weighs about 0.345 oz (9.5-10 g). The adult male has an olive-green back, and its face and breast are black apart from a bright yellow throat, supercilia, and lower eyelid spot. The rest of the underparts are greyish olive.

The adult female is dull olive-green above and paler grey below, and may have some dark breast smudges. The face pattern is much weaker and duller, and may be almost invisible. Young birds are like the adult female but duller and greyer. Young males begin to acquire full adult plumage in their first year.

The Yellow-faced Grassquit has a weak buzzing trilled ttttt-tee call.

It is a common to abundant resident in lowlands and foothills up to 7,500 ft (2,300 m) altitude in semi-open areas such as roadsides, pasture, weedy fields, low scrub and gardens. It sometimes forms loose flocks with other tanagers and emberizids which share its lifestyle. This species feeds mainly on grass seeds, but also takes other seeds, berries and some insects.

During courtship, the male vibrates his wings as he sings his subdued song, sitting only 1-2 in (a few cm) away so she can properly hear him. The globular nest, built by the female, is made of grass and weed stems and lined with finer material. It has a side entrance and is placed usually less than 1 ft (30 cm) above the ground, often on a grassy bank. This species sometimes forms loose colonies. The clutch is two or three brown-speckled white eggs, which are incubated by the female alone for 12-14 days to hatching.

This bird is not rare and widely distributed; it is thus classified a Species of Least Concern by the IUCN. It seems to benefit from deforestation, increasing in numbers and expanding its range; for example, it is only since 1997 known from the eastern Andean slope of Meta Department in Colombia.