The 45-year-old Ryan, seated with his arms crossed, had the beard in a photo on Twitter that posed the question, "Hey @USHouseHistory, when was the last time a Speaker of the House sported a beard?"
The answer: Speaker Joe Cannon of Illinois, a Republican who led the House from 1903-11, and Republican Frederick Gillett of Massachusetts, who led the House from 1919-25.
Ryan succeeded a beardless John Boehner, who stepped down as speaker in October.
It was unclear whether Ryan would shave or not. His office said he would keep the beard as long as his wife, Janna, let him.