Abstract: In an acetate buffer solution of pH 5.5 and in the presence of sodium dodecyl benzene sulfonate, enhancement of fluorescence intensity of rhodamine B was observed due to the occurrence of energy transfer between eosin Y and rhodamine B. It was shown further that when under a temperature of 40 ℃ and in the presence of trace amounts of Mn(Ⅱ), the fluorescence of rhodamine B emilted at 576 nm was quenched and that linear relationship was obtained between the magnitude of the fluorescence quenching, ΔF which is the difference of fluorescence intensity of the test solution without Mn(Ⅱ), F₁ and of that with Mn(Ⅱ), F₂ measured at λ_ex=508 nm and λ_em=576 nm and the concentration of Mn(Ⅱ) ion in the range of 1.0×10^-8-2.0×10^-7mol·L^-1, with detection limit (3s/k) of 4.0×10^-9mol·L^-1. Based on these facts, a method of fluorescent spectroscopy determination of trace amount of Mn(Ⅱ) in samples was proposed. Tests for precision and recovery (by standard addition method) were performed by analyzing a substantial sample with the proposed method, giving values of RSD (n=11) of 4.8% and of recovery of 106%.