This paper reports on performance enhancement of polymer light-emitting diodes (PLEDs) based on poly(2,5-bis(3′,7′-dimethyl-octyloxy)1,4-phenylene-vinylene) (BDMO-PPV) after Indium Tin Oxide (ITO) pre-treatment. Diluted aqua regia surface treatments of ITO substrates were investigated before PLEDs manufacturing. The correlation between ITO surface morphology and the properties of devices were discussed. The residual roughness, the global ITO thickness and developed anodic active area were found extremely dependent on treatment time. The performances of the ITO/BDMO-PPV/Ca/Al diodes were improved. With long treatments, the roughness was dramatically increased and poor PLEDs performances were achieved. The incorporation of a conducting polymer layer, poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonate, between the ITO layer and the emissive polymer, was also studied. With this buffer layer, no effect of the acidic treatment was observed on luminance–voltage characteristics and low turn-on voltage devices were made.