It comes a day after the North fired its own ballistic missile into the Sea of Japan -- which analysts dubbed a warning ahead of a China-US summit, at which Pyongyang's accelerating atomic weapons programme is set to top the agenda.
South Korea is protected under an American security umbrella and is home to thousands of US troops.
But in 2012 it reached an agreement with the United States to almost triple the range of its ballistic missile systems to guard against the North's nuclear threats, and has since been developing missiles with longer ranges.
Citing a high-ranking government official, Yonhap said the South's missile with a range of 800 kilometres (500 miles) could serve as a strong deterrent to Pyongyang.
"The test-firing was successful", the official was quoted as saying.
A defence ministry spokesman declined to comment.
The South plans to deploy the new missile this year following further tests to determine its reliability, Yonhap said.
The new missile could cover all of North Korea even when fired from a southern region of the country, it said.
In June last year, the South successfully test-fired two home-developed missiles capable of carrying a one-tonne payload up to 500 kilometres.
Pyongyang's nuclear weapons programme is likely to dominate when US President Donald Trump meets China's leader Xi Jinping at his Mar-a-Lago estate in Florida Thursday, their first face to face meeting.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)