The measures apply to three businesses associated with the Sudanese Armed Forces (SAF) and three to its rival in the power struggle, the Rapid Support Forces (RSF).
The action comes with the conflict between the regular army and the RSF threatening to spiral into a full-blown civil war.
Foreign Secretary James Cleverly said: “These sanctions are directly targeting those whose actions have destroyed the lives of millions, according to reports.
“Both sides have committed multiple ceasefire violations in a war, which is completely unjustified.
The Foreign Office said around 25 million people had been left in need of humanitarian assistance as a result of almost three months of violence, with more than 2.2 million internally displaced.
The companies associated with the RSF identified by the Foreign Office are: Al-Junaid, GSK Advance Company Ltd and Tradive General Trading Co.
The three SAF-linked firms are: Defense Industries Systems, Sudan Master Technology and Zadna International Company for Investment.
The sanctions will ensure that any assets held by the firms in the UK will be frozen.