The countdown got down to the 40-second mark, but it was halted because of issues with the 123-metre rocket.
A test flight for SpaceX's Starship mega rocket was delayed on Monday due to last-minute problems.
"Standing down from today’s flight test attempt. Starship team is determining the next best available opportunity to fly," SpaceX wrote in a social media post.
The countdown got down to the 40-second mark but was halted because of issues with the 123-metre rocket, the world’s largest and most powerful.
Starship was supposed to blast off from the southern tip of Texas with four mock satellites on board for a space-skimming test flight.
If the problems can be fixed quickly, another launch attempt could come on Tuesday, according to SpaceX.
The last Starship test flight ended in an explosion over the Atlantic in January, with flaming debris streaming over the Turks and Caicos.
Starship has already been booked by NASA for astronaut moon landings later this decade.
SpaceX's Elon Musk intends to use the mammoth rockets to settle Mars.