"Today's launch of the Atlas V 501 rocket with the United States Space Force-7 mission featuring the X-37B Orbital Test Vehicle was postponed due to inclement weather conditions", ULA said in a statement.
The rocket is scheduled for take-off from Cape Canaveral in the US state of Florida at 9:14 a.m. EDT (13:14 GMT) on Sunday.
"Darn weather. See you tomorrow. Going to need everyone to focus on those calm, clear thoughts even harder", ULA CEO Tony Bruno tweeted.
The US Space Force, the newly created branch of the US military, is overseeing the X-37B mission. The Air Force said the plane was carrying a small satellite built by the Air Force Academy. The purpose of other experiments is not known.