The last time that a unified Korea team played the world table tennis championships was 1991 in Chiba, Japan, where the women's team shocked defending champions China to win the gold medal.
The decision to form a unified team was a tripartite agreement between the leaders of the North and South Korean Table Tennis teams and the ITTF.
"I'm happy. It's a bit of a risk of course as this is not 100 percent according to the rules," ITTF president Thomas Weikert told Reuters after a news conference.
"But there's no disadvantage to the teams before and we informed all the (other) teams and they agreed... we all feel happy that we have a small sign in the process of the reunion of Korea.
"We respect the rules, yes we changed them, but we will never do that again, and it's more than a sport, it's more for the peace... I think it's worth it."
Japanese player Mima Ito said a unified Korea would not necessarily pose a greater challenge to them in the last four.
"It doesn't really matter, we play our own game, we play our own system. We are looking at our own game and not our opponent," she said.
"The other team has five players, so it's the same. We really concentrate on our game - we will do what we want to do. That's what we plan to do."
The move follows the North and South Korean leaders' pledge to work for "complete denuclearisation" of the Korean peninsula last week.
The two Koreas had earlier this year joined forces to field a combined women's ice hockey team at the Pyeongchang Winter Games after they marched together for the opening ceremony.
(Reporting by Hardik Vyas in Bengaluru; Additional reporting by Phil O'Connor in Stockholm; editing by Pritha Sarkar and Christian Radnedge)
