The 27-year-old made six appearances in his month-long stay with the Iron, scoring one goal in the 1-1 draw with Walsall earlier this month.
The former Cheltenham striker was originally drafted in to provide cover for Ben May, but with May now fit again, boss Nigel Adkins has decided against extending Odejayi's spell with the club.
"Big Kay is going back to Barnsley and we thank him very much for all his efforts," Adkins told his club's official website.
"He's been unfortunate but Ben May is now fit again so it all ties in nicely.
"Barnsley are in a relegation battle and need all their players available. Kay has been outstanding and has been a model professional."