White polymer light emitting diodes (WPLEDs) with a glass/ITO/PEDOT:PSS/PVK:PFO:MDMO-PPV/TPBI/LiF/Al structure were fabricated to investigate the effects of the doping concentration of MDMO-PPV emission materials. The PVK, PFO and MDMO-PPV conjugated polymers as host and guest emission materials were spin coated at various concentrations of MDMO-PPV ranging from 15.0 to 30.0 vol%. As the concentration of MDMO-PPV increased from 15.0 to 30.0 vol%, the luminance and current efficiency values were decreased clearly, which are attributable to the quenching effect at a high doping concentration. The maximum luminance and current efficiency were 2280 cd/m2 and 3.83 cd/A, respectively for a WPLED with 15.0 vol% of MDMO-PPV. The average CIE color coordinates were about x = 0.33, y = 0.37 at 15 V, showing a white emission color.