In　this　paper,　we　consider　the　density　estimation　problem　from　independent　and　identically　distributed　(i.i.d.)　biased　observations.　We　study　the　lower　bound　of　convergence　rates　of　density　estimation　over　Sobolev　spaces　WrN(N{cyrillic,　ukrainian}N+　under　the　Lprisk　by　using　Fano＇　s　lemma.　©　(2013)　Trans　Tech　Publications,　Switzerland.