An organic light emitting device (OLED) with brightness uniformity design comprises a substrate, an anode layer, a light emitting layer, a cathode layer, a plurality of anode leads and a plurality of cathode leads. The anode layer has a plurality of separate regions formed on the substrate respectively; the light emitting layer has a plurality of separate regions formed on the plurality of anode layer regions respectively; the cathode layer has a plurality of separate regions formed on the plurality of light emitting layer regions respectively. The anode leads with different cross-sectional areas are respectively connected to the regions of the anode layer, and the cathode leads with different cross-sectional areas are respectively connected to the regions of the cathode layer; the anode leads are connected to a positive input terminal of a power supply, and the cathode leads are connected to a negative input terminal of the power supply. The ratios of the lengths to the cross-sectional areas of the anode leads and cathode leads are the same, such that the currents flowing through the regions of the light emitting layer are the same.