Abstract: In this paper, the interactions between acenaphthene (AC) and 1,4-dicyano- benzene(p-DCB) and between AC and 1, 3-dicyanobenzene(m-DCB) were studied. The results show that both systems can form exciplex but the peak positions of the two exciplex are different. For AC-pDCB, the peak position of exciplex is si- tuated at 420-425 nm but for AC-mDCB, it is around 410-415 nm. These facts indicate that the interaction between AC-pDCB is stronger than AC-mDCB. On the other hand, fluorescence quenching of acenaphthene by DCB are deviated from Stern-Volmer rule at higher concentrations of DCB. This phenomenon can be explained by the principle of sphere of action. Radius of action sphere are 1.4 nm and 1.2 nm respectively for AC-pDCB and AC-mDCB. Fluorescence decays of AC at different concentrations of pDCB or mDCB were also measured. Single exponential decay formula is obeyed for all of the measurements. From the experimental data of fluorescence decay, k_3/k_4 of both systems were calculated.