The missile, is their second missile test in the space of seven days after launching their most successful missile test last week.
The missile flew about 500km and it is believed to have landed in waters off South Korea's east coast, South Korea's military said.
New South Korean President Moon Jae-in, reacting to the missile launch, held a National Security Council meeting- this is the second launch test North Korea has had in Moon's short time as president, while the White House said the missile had "a shorter range than the missiles launched in North Korea's three most recent tests".
In a statement, South Korea's Joint Chiefs of Staff said they were at "full military readiness" and were "closely monitoring signs for additional provocation by the North Korean military". On Sunday, North Korean state newspaper Minju Joson threatened more missile launches against the United States.
Minju Joson said: "If the US persists in confrontation with the DPRK (North Korea), the latter will show how the crime-woven history of the US is put to an end.
"Many more weapons capable of striking the US will be launched from this land. This is the DPRK's answer to the Trump administration."