Aggregation of some nitrogen-containing heterocyclic compounds have been investigated by means of fluorescence spectroscopy in aqueous or aquiorgano binary mixtures of different φ values for the first time. The aggregators studied are Nbutylcarbazole (CBZ-4), N-octylearbazole (CBZ-8), N-dodecylcarbazole (CBZ-12), and N-hexadecylcarbazole ( CBZ16). Their aggregating tendencies have been evaluated by measuring their critical aggregate concentration values (CAgC's). Our results indicate that the N-alkylcarbazoles,just like the anthracene derivatives with different chain lengths, can also be used as fluorescence probes for evaluating aggregating tendeneies or CAgC values.