The study on the interaction of BPLA₂ with Ca^2＋ by fluorescence spectroscopy indicated that Ca^2＋ was very important to BPLA₂.In the prescence of Ca^2＋ ,the environment around the Trp residue in BPLA₂ became more hydrophobic upon the binding of the substrate to the enzyme,resulting in 9 nm blue shift of the Trp fluorescence emission spectrum. But such a phenomenon was not observed in the absence of Ca^2＋.The experiment indicated that there was a hydrophobic region in BPLA₂ molecule. Ca^2＋ might increase the hydrophobility of this region. Further，it was also found that the binding of Ca^2＋ to the enzyme was related to the single His residue of the enzyme.