The King dismissed the two officials and a host of other commanders in a major shake-up, Gulf News on Monday cited a series of royal decrees as showing.
"Termination of the services of General Abdul Rahman Bin Saleh Al Bunyan, Chief of Staff," it said, adding that Fayyad Al Ruwaili had been appointed as his replacement.
The monarch also replaced the heads of the ground forces and Air Defence.
No official explanation was given for the replacements, which come as the kingdom's bloody conflict with the Iran-backed Al-Houthi rebels nears the end of its third year.
A Saudi-led coalition supporting Yemen's government has been fighting the Al-Houthis since 2015.
Crown Prince Mohammad Bin Salman, the heir to the throne and the son of the monarch, is the country's Defence Minister.(ANI)