Ionic liquids have recently been used as solvents for biphasic atom transfer radical polymerization (ATRP) to facilitate the separation of the products from the catalysts. Here we report an ionic liquid catalyst for biphasic ATRP of MMA to greatly reduce the amount of ionic liquid needed and to reuse the catalyst: CuBr/N,N,N '',N ''-tetraethyldiethylenetriamine (TEDETA) anchored on an imidazolium-based ionic liquid (BITT) formed an ionic liquid catalyst insoluble in the mixture of MMA and toluene but could be easily dispersed in the reaction media. With the catalysis of CuBr/TEDETA-BITT, the polymerization of MMA at 60 degrees C was well-controlled, producing polymers with high initiator efficiency and low polydispersity (similar to 1.2-1.4). Once the stirring was stopped, the catalyst easily settled on the bottom of the reactor as a thin liquid layer, and thus the catalyst was easily isolated from the polymer solution. After regeneration, the recycled catalysts catalyzed the second run polymerization with similar or even higher activity and improved control. The residual catalyst concentrations in the polymers were in the range 50-100 ppm. The addition of a small amount of silica gel to the polymer solution could further reduce the residual catalyst concentration.