Light scattering and viscosity measurements on micellar solutions of block copolymers were carried out in the presence of polyisobutylene. Micelle size and molar mass were determined for micelles of polystyrene-block-poly(ethylene/propylene) in 5-methyl-2-hexanone and 2-pentanone and for micelles of polystyrene-block-poly(ethylene/butylene)-block-poly styrene in 3-methyl-2-pentanone in the presence of different percentages of polyisobutylene. As the percentage of homopolymer solubilized in the micellar increases, the size and the aggregation number of the micelles become larger. The temperature effect on micellar solutions was also studied. The presence of homopolymer in the micelle solutions causes the so-called anomalous behavior. This becomes more intense as the molar mass or the percentage of the homopolymer increases.