A structure of a scanning window of an image scanning device has a housing, a transparent platen, a plurality of bases and a plurality of supporting blocks. The bases are formed on the inner walls of the housing. The supporting blocks are disposed on the bases and each supporting block has a supporting part. The transparent platen is disposed between the top portion of the housing and the supporting parts. Thus, the transparent platen is fixed in place by the supporting parts and the top portion of the image scanning device.