Amoroso will be replaced in the chairman role by director Maynard Webb Jr on an interim basis until the company's annual shareholder meeting on June 25.
Amoroso, a former IBM Corp executive, will remain on the board of directors until the meeting, Yahoo said.
In a statement on Thursday, Amoroso said he had informed the Yahoo board when he became chairman in May 2012 that he intended to serve only one year "in order to help Yahoo during a critical time of transformation."
Since that time, he noted that the company has hired former Google executive Marissa Mayer as its chief executive, revamped its management team and released new products.
Shares of Yahoo, which have surged roughly 60 percent since Mayer became CEO, were down 8 cents to $25.12 in afterhours trading on Thursday.
Yahoo, once one of the Web's most successful companies, has seen its revenue stall in recent years as consumers and advertisers favor rivals such as Google Inc and Facebook Inc.
Following the completion of Amoroso's term at the annual meeting, the Yahoo board will consist of 10 members, the company said.