An objective optical system for endoscopes is provided for the purpose of carrying out a fluorescence observation. At least two excitation light cutoff filters in which the transmittance of excitation light in its wavelength band is 0.1 % or less are arranged and an optical element with power is interposed between arbitrary two of the excitation light cutoff filters. Whereby, the leakage of the excitation light caused by oblique incidence on the excitation light cutoff filter can be effectively prevented and even the feeble fluorescent light can be observed without flare with respect to the excitation light.
