The 21-year-old, who joined Chelsea in January 2012, spent last season on loan at English Championship side Middlesbrough, making 22 appearances.
His switch comes after a vow to fight for a place at Chelsea this season.
"The target is to get a lot of playing time and help Kasimpasa achieve their objectives," he told BBC Sport.
"I've come to Turkey to reciprocate the club's determination to bring me here. I want to show the manager and the fans that they have made a good choice and I am completely focused on breaking into the squad and prove myself here.
"They have strong faith in my ability and I need to prove it. Last season was difficult because of injuries which affected me both at club and international level but I have put all that behind me.
"Kasimpasa approached Chelsea in a professional manner and the chance to test myself in a top league is very challenging."
Omeruo underwent his medical at Kasimpasa on Tuesday before signing a deal, which includes an option for the Turkish club to buy him at the end of the loan.
He joined Chelsea from Belgian side Standard Liege in 2012 and developed on loan at ADO Den Haag in Netherlands in an 18-month spell from 2012 to 2013.
Omeruo made 14 appearances in his first loan spell at Boro after joining in January 2014 and returned for the whole of last season.
The centre-back was first called up by Nigeria in January 2013 and he went on to play at that year's Africa Cup of Nations and Confederations Cup - and at the 2014 World Cup.
Nigeria international defender Kenneth Omeruo has joined Turkish Super Lig side Kasimpasa on a season-long loan deal from English champions Chelsea.