This paper reports the excited-state upconversion of Pr(0.5):ZBLAN glass under two-color excitation. It is found that the fluorescence of upconversion-emiss ion spectrum is the same as that of common-emission spectrum. It is found also that there are three obvious peaks on upconversionexcitation spectrum under twocolor excitation, which corresponds to the 788.5nm 1G4→3P2,850.5nm 1G4→1I6,and 805.0nm 3H6→1D2 excited state absorpt ion transitions res pectively. The large 850.5nm peak of upconversion-excitation spectrum results from the large 1G4(Pr3+ )→1I6(Pr3+) (Pr3+) oscil lator strength f=23.04×10-6. It illustrates the excited state absorp tion upconve rsion from 1G4 level, especially the 1G4(Pr3+)→1I6(Pr3+) upconversion process is large. It results in the upcon version luminescence of Pr(0.5):ZBLAN under two-color excitation.