Right-back Aina is the first player to make what is likely to become a well-trodden path from Stamford Bridge to Humberside, with new Hull boss Leonid Slutsky known to be keen to capitalise on his good relationship with Chelsea owner Roman Abramovich.
Their friendship is expected to lead to more Blues youth products heading to the KCOM Stadium during the close season.
"I'm very excited to be here and it is the start of a new chapter in my career," Aina told Hull's official website.
"It's my first loan move away from Chelsea and I just want to hit the ground running.
"I'm looking forward to getting to know all of my new team-mates during the training camp in Portugal."