In　this　paper,　we　consider　the　density　estimation　problem　from　independent　and　identically　distributed　(i.i.d.)　biased　observations.　We　develop　an　adaptive　wavelet　hard　thresholding　rule　and　evaluate　its　performance　by　considering　risk　over　Sobolev　balls.　We　prove　that　our　estimation　attains　a　sharp　rate　of　convergence　and　show　the　optimality.　MSC:　49K40,　90C29,　90C31.