With her face and body completely covered by the black head-to-toe abaya mandatory in the conservative Muslim kingdom, 18-year-old Mullah was named "Queen of Beautiful Morals" late on Thursday, newspapers said.
There was none of the swimsuit and evening gown competitions and heavy media coverage of beauty pageants elsewhere when the contest was decided in the eastern city of Safwa.
Instead, the winner and the two runner-up princesses had to undergo a three-month test of their dutifulness to their parents and family, and their service to society.
This included a battery of personal, cultural, social and psychological tests, Al-Watan reported.
It was unclear exactly what Mullah did to pip her rivals in the huge field, but Al-Watan reported that the high school graduate had good grades and hopes to go into medicine.
She raked in a 5,000-riyal (1,333-dollar) prize, a pearl necklace, diamond watch, diamond necklace, and a free ticket to Malaysia with her win.
The 20-year-old first runner-up, one of triplets, had already won an education ministry-sponsored "I love you, my country" competition.
The second runner-up, a high school student aged 15, was cited for taking care of her home and family during the week because her mother works far from home and can only return on weekends.
Beauty contests focused on physical beauty are non-existent in segregated Saudi Arabia, where women can not mix with unrelated men, and must appear in public completely covered, even in photographs.
Miss Moral Beauty pageant organiser Khadra al-Mubarak kept the focus on inner beauty, as defined by Islamic standards of Saudi Arabia.
"The real winner in this competition is the society. The winners represent the culture of the society and its high Islamic morals," Mubarak said, according to Al-Watan.