The 17-year-old Karate champ made history after defeating Japanese Masaki Yamaoka with an 8-0 win.
The kingdom had a great run at the two-week youth Olympics، also taking home two bronze medals in weightlifting and 400m hurdles.
In a statement on the wins, Yousef Jalaiden, head of the Olympic mission for the Saudi delegation, said:
"We are very happy right now. It's our best achievement ever at an Olympics — be it Youth or the full Olympics."
"I have been working towards this moment for 10 years"
In a statement he gave to press after his win, Al-Assiri expressed his happiness at the achievement.
"I am so happy, so proud. This is the first gold medal for Saudi Arabia and our first medal ever in karate," he said.
"I have been working towards this moment for 10 years, especially in the past two when my training intensified. I came for gold and this is the result of years of serious work. It was very difficult, but I am just so proud. Thank you to Allah," he added.
Saudis are overjoyed with the win
"A special moment for Saudi sport"
Al Assiri deserves the recognition
"Congratulations to our hero Mohammed Al Assiri. He deserves this medal."
Everyone is proud of the young man