Provided is a biosensor that uses multiple organic light emitting diodes (OLEDs) as light sources. The biosensor includes a transparent substrate, a plurality of OLEDs which are disposed on a first surface of the transparent substrate and are electrically separated from each other, and a photo detector above the transparent substrate that receives light emitted from a specimen disposed on the transparent substrate, wherein the specimen is disposed on a region of a second surface which is a surface opposite to the first surface of the transparent substrate.