The locations and numbers of solubilized pyrene molecules in heptaethyleneoxide monoalkyl ether CnE7 (n = 10, 12, 14, and 16) surfactant micelles were studied as functions of the alkyl chain length, micelle concentration, aggregation number, and pyrene concentration by means of steady-state fluorescence spectroscopy. It was found that the monomeric fluorescence intensity ratio of the third to the first vibrational bands of pyrene in the micelles depends on the volume of the hydrophobic core, that is, the alkyl chain length. The ratio of pyrene excimer fluorescence intensity to the intensity of the first vibrational band (I-e/I-m1) was found to increase with the CnE7 micelle concentration and to reach a maximum ratio at a particular micellar concentration. The micellar concentration at the maximum value of I-e/I-m1 depended on the alkyl chain length and shifted to a lower micellar concentration when the alkyl chain length increased. The number of solubilized pyrene molecules in the unit core volume at the maximum value of I-e/I-m1 was found to be linearly proportional to the aggregation number of the micelles.