Automated searches for minimum energy conical intersection structures between the lowest two singlet electronic states (S-0/S-1-MECIs) of furan and dibenzofuran were made. In total, eight and sixty S-0/S-1-MECIs were found for furan and dibenzofuran, respectively, around their Franck-Condon (FC) regions. The difference in their experimental fluorescence quantum yields was discussed based on the barrier heights to reach S-0/S-1-MECIs from the FC regions. It was found that the stability of the FC region is the major factor giving the difference in their fluorescence quantum yields.