ABSTRACT The effect of pressure on the fluorescence of tryptophan in the presence of metal ions was studied by fluorescence spectrometry. It was found that at 60 MPa, the fluorescence intensity of M/Trp mixtures (M represented metal ions) increased compared to that at atmosphere pressure. The relative fluorescence efficiency of M/Trp mixtures increased with pressure. When the M/Trp ratio was above 10:1, the relative fluorescence efficiency in decreasing order was Cu2+/Trp mixtures, Ni2+/Trp mixtures and Mg2+ (K+)/Trp mixtures. When the ratio was below 10:1, the decreasing order was Cu2+/Trp mixtures and Ni2+ (Mg2+, K+)/Trp mixtures. The relative fluorescence efficiency increased with the concentration of Cu2+ and Ni2+. The variation was relate to the quenching of tryptophan fluorescence in the presence of metal ions. A red shift was also observed, but the red shift was independent of metal ions.