The newly-promoted Premier League club have an option to turn the 23-year-old’s loan into a permanent move at the end of this season.
Nigeria international Aina is back in London, where he was born and spent several seasons in Chelsea’s youth team before joining Torino.
“I feel very excited and privileged to be able to play for a club like this,” Aina told Fulham’s website. “It feels amazing to be back closer to my family, back in the capital where I was born and raised. There’s a great bunch of lads here. I’m really good friends with Big Hec (Michael Hector) and Josh Onomah.”
Aina joined Chelsea aged 11 and went on to make three league appearances between 2015 and 2019. After impressing in Italy on loan, Torino signed Aina on a permanent basis.
Fulham open their Premier League campaign at home to Arsenal on Saturday.