Astronomers say that they have spotted two Earth-sized worlds orbiting a Sun-like star.
One of the planets is just 3% bigger than Earth and the other is 13% smaller, which would make it a bit smaller than Venus.
The discovery was made by astronomers from the universities of Toulouse, France, and Montreal, Canada. Details are outlined in Nature journal.
The BBC's science correspondent reports they are the smallest exoplanets to be found since the first world beyond our solar system was officially detected in 1995.
The planets are inferred to have a rocky composition similar to Earth's.
Both planets are thought to be too hot to be capable of supporting life because they orbit so close to their star, Kepler-20.
But according to Dr Francois Fressin, of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, USA, the planets were once further from their star and cool enough for liquid water to exist on their surface, which is a necessary condition for life.