Previous investigations on the constitution and phase of the binary system Ir-B revealed the existence of three compounds Ir3B2, IrB and IrB2.However, due to the experimental difficulties in identifying the boron atoms, many arguments on those compounds exists.In combination with X-ray single crystal and powder diffraction analyses and first-principles calculations, we have reinvestigate the crystal structures and constitution of the Ir-B phases.Four binary phases have been found, namely Ir4B5+x, Ir5B4+x and the high and low temperature modification of Ir4B3-x.X-ray structure analyses have been performed on single crystals of Ir4B5+x (x=0, Ir4B5 type;space group C2/m;a =1.05200(2), b =0.289564(6) and c =0.60958(1)nm, β =91.156(2)°), Ir5B4+x (x=0, Ir5B4 type;space group I41/a;a =0.62777(1) and b =1.02599(2) nm)and on the low temperature modification of Ir4B3-x (x=0, IrB0.9 type;space group Cmc21;a =0.27728(1),b =0.75742(2) and c =0.73152(2) nm).The high temperature modification of Ir4B3-x (WC type;space group P m2;a =0.28137(5) and c =0.2828(1) nm) has been confirmed by X-ray powder diffraction More details on their structural stabilities, phase transition and mechanical properties will be discussed.