It has been observed that a small magnetic field influences the luminescence intensity of the trans-anethole-9-cyanophenanthrene exciplex (AN : CNP) in a polar solvent. The variation of the effect with the wavelength of luminescence, the magnetic field strength and the dielectric constant of the solvent mixture has been discussed. The luminescence yield decreases monotonically with the dielectric constant of the mixed solvent, while the percentage change in luminescence intensity on application of the magnetic field goes through a maximum. With identical series of solvent mixtures having alcohol as one component, the maximum magnetic field effect occurs at ε= 38 as against ε= 28 for the pyrene–dimethylaniline system; this shift of ε_max has been explained with the help of a schematic diagram and correlated in a qualitative way with the degree of charge transfer in the exciplex.