The critical concentration c* was measured using both fluorescence excitation spectroscopy and light scattering for four narrow molecular weight distribution samples of polystyrene (MW = 225,000 – 1,500,000) in bicyclo[4.4.0]decane (decahydronaphthalene, decalin) at 20ºC and 30ºC. A discontinuity in the corrected intensity of a band in the excitation spectrum (assigned to the dimmer complex) as a function of concentration allowed determination of the critical concentration, c*, from the excitation spectra. The c* results from fluorescence and light scattering were identical within experimental error and were comparable to c* values calculated from literature methods. Fluorescence excitation spectroscopy should be a convenient method for determining c* for aromatic polymers.