The attack came a day after similar air strikes killed around 50 people and as Persian Gulf Arab ground forces seek to advance against the Houthi fighters who hold the capital, Sana'a.
"Two missiles hit the two houses in the Asbahi district in southern Sana'a, destroying them, killing 20 people and wounding others," a medic at the scene said, according to Reuters.
A local official had earlier said that a hotel in the same district had been hit.
An alliance of Persian Gulf Arab states - mostly the wealthy neighbours of impoverished Yemen on the Arabian Peninsula - attacked the country in late March to restore fugitive former president Abd-Rabbu Mansour Hadi.
Ground troops of the coalition countries are now trying to push into Houthi strongholds in northern Yemen and in Sana'a, which the group seized a year ago. So far, they appear to have made few gains.
Saba, the Houthi-controlled state news agency, said 236 people have been killed in air strikes over the last four days.