A new fluorescent deoxycytidine analog, 10-(2-deoxy-beta-D-,ribofuranosyl)-pyrimido[1,5:4,5]pyrimido[l, 6-a]indole-6,9(7H)-dione (dC(PPI)) was synthesized. Its fluorescent properties were studied in detail. It was found that this fluorescent nucleoside dC(PPI) could be used as a fluorescent label for DNA probes with minimal disturbance of their overall structure.