Natoga can play at centre, wing or full-back and has won five full caps for his country, scoring one try.
The 22-year-old, joining from Fijian side Nadroga, is currently awaiting Home Office visa clearance.
Ospreys rugby operations manager Andy Lloyd told the club's website: "We've been tracking Aisea for some time so we are delighted to be able to secure his services for the Ospreys.
"He fits what we are trying to do here as a team that remains ambitious to compete on all fronts. He adds another edge to our backline and gives us depth in key positions that we didn't have last season.
"Although he's played sevens rugby he isn't just a stereotypical side-stepping sevens player, he has physicality and power which makes him a very dangerous player. He's versatile and positionally he has good awareness of what is happening around him."
- Sports & Recreation