Lukaku joined Albion for the entire campaign although Chelsea had the option to recall the player this month.
But the deadline to take Lukaku back to Stamford Bridge expired on Monday.
Lukaku has been in fine form, netting seven goals and being preferred to Shane Long as the lone central striker in some of the Baggies' recent matches.
A West Brom club spokesman confirmed: "Roman will remain at the Hawthorns for the rest of the season.
"Chelsea's January option to recall him expired on Monday."
Lukaku recently made it clear that he believes staying at Albion is important for his development at this stage of his career rather than being a bit-part player at Chelsea.
He also indicated that he would like to return on loan to the Hawthorns for next season before going back to the Blues.