Abstract: The state of Sn in reforming catalysts was studied by MÖssbauer spectroscopy. The catalysts were prepared by both co-impregnation and co-precipitation methods. Besides the effect of different Pt/Sn atomic ratio on the state of Sn,the state of Sn after calcination,reduction or reaction was also investigated.After reduction, Sn in the catalysts prepared by co-impregnation method exists in various forms: tetravalence(SnAl₂O₅,SnO₂),divalence(SnAl₂O₄,SnO)and Sn/Pt alloys(Pt₃Sn, Pt Sn₄).The amount of tetravalent tin remains constant while the amount of divalent tin increases with the increasing total amount of Sn(the amount of Pt is kept constant).As for the catalyst prepared by co-precipitation method,most of Sn exist in one state after reduction:tetravalence(SnAl₂O₅,SnO₂);and this tetravalent tin increases proportionally with total amount of Sn in the catalyst. For catalysts prepared by co-impregnation method,the change of the state of Sn after calcination,reduction or reaction is significant,i.e.,some of tetravalent tin(SnAl₂O₅,SnO₂)after calcination is changed to divalence and alloy form, but all of them changed to SnO₂ after reaction.Sn in the catalyst prepared by co-precipitation method remains tetravalence(SnAl₂O₅,SnO₂),but its size is changed.It is believed that ionic tin is beneficial to the performance of Pt/Al₂O₃ reforming catalyst.