A fastener-driving sleeve assembly adapted to be driven by a rotary driving tool to thereby rotate a fastener, the rotary driving tool having a non-circular driving head, said fastener-driving sleeve assembly including: a connecting sleeve made of metal and having a tool-connecting portion and a fastener-connecting portion, said tool-connecting portion having a head-receiving hole adapted to engage fittingly the driving head of the rotary driving tool so as to allow for co-rotation of said connecting sleeve with the driving head, said fastener-connecting portion having a fastener-receiving hole adapted to engage fittingly the fastener so as to allow for co-rotation of the fastener with said connecting sleeve; and a reinforcing ring made of metal and sleeved fixedly on said fastener-connecting portion of said connecting sleeve, said reinforcing ring and said connecting sleeve having complementary interengaging surfaces, said reinforcing ring and said connecting sleeve being made of two different metal materials, respectively; characterized in that said fastener-connecting portion of said connecting sleeve further has a flange extending radially and outwardly therefrom to define an annular large shoulder surface, and a frustoconical intermediate portion defining an annular small shoulder surface facing said large shoulder surface; and that said reinforcing ring abuts against said large shoulder surface at an end thereof, and defines a central bore having a frustoconical intermediate portion that engages fittingly said frustoconical intermediate portion of said connecting sleeve, said reinforcing ring having an annular shoulder surface that defines an end of said frustoconical intermediate portion of said central bore and that abuts against said small shoulder surface of said connecting sleeve so as to prevent removal of said reinforcing ring from said connecting sleeve. a connecting sleeve made of metal and having a tool-connecting portion and a fastener-connecting portion, said tool-connecting portion having a head-receiving hole adapted to engage fittingly the driving head of the rotary driving tool so as to allow for co-rotation of said connecting sleeve with the driving head, said fastener-connecting portion having a fastener-receiving hole adapted to engage fittingly the fastener so as to allow for co-rotation of the fastener with said connecting sleeve; and a reinforcing ring made of metal and sleeved fixedly on said fastener-connecting portion of said connecting sleeve, said reinforcing ring and said connecting sleeve having complementary interengaging surfaces, said reinforcing ring and said connecting sleeve being made of two different metal materials, respectively; characterized in that said fastener-connecting portion of said connecting sleeve further has a flange extending radially and outwardly therefrom to define an annular large shoulder surface, and a frustoconical intermediate portion defining an annular small shoulder surface facing said large shoulder surface; and that said reinforcing ring abuts against said large shoulder surface at an end thereof, and defines a central bore having a frustoconical intermediate portion that engages fittingly said frustoconical intermediate portion of said connecting sleeve, said reinforcing ring having an annular shoulder surface that defines an end of said frustoconical intermediate portion of said central bore and that abuts against said small shoulder surface of said connecting sleeve so as to prevent removal of said reinforcing ring from said connecting sleeve.