Flexible organic light-emitting diodes(FOLEDs) with ITO/PVK:TPD/Alq_3/Al configuration prepared on poly ethylene-tane-phthalate(PET) substrates were fabricated.The curves of the current density-voltage,optical current-voltage and quantum efficiency-current density of the devices were investigated.Compared to those with glass substrates fabricated under the same conditions,the opening voltage of the FOLEDs was a little higher than them,but those characteristics of two kinds of devices were very similar.Under the driving voltage of 20 V,the corresponding brightness and quantum efficiency were 1 000 cd/cm~2 and 0.27%.