Rotational motion of chlorobenzene (CB) in poly(methyl methacrylate) (PMMA) over a range of temperature and chlorobenzene concentration is studied by the depolarized dynamic light scattering technique. It was found that the depolarized spectrum of chlorobenzene in PMMA at concentrations of 20 g of chlorobenzene/ 100 mL or greater shows two widely separated sets of relaxation times, one “fast” on the neat-CB time scale (few picoseconds) and another in the nanosecond and longer time scale (relaxation times typical of macromolecules). The scattered light intensity ratio of the fast to the slow component of the relaxation times was found to increase exponentially with both temperature and concentration. The fast rotational relaxation time was also found to be temperature and CB-concentration dependent. © 1980, American Chemical Society. All rights reserved.