Uridine and adenosine were excited to the first electronically excited state)using the the output of a frenquency-quadrupled Nd: YAG laser(266 nm),and interactedwith the phenylalanine in the mixed solution with equal mol-concentration. Because of thedifference of molecular polarization and structure between the excited uridine andadenosine, the efficiency of exciplex formation and the energy-transfer efficiency betweenthese two kinds of nucleosides and phenylalanine are different,yielding remarkable differences of the fluorescence spectra.