In this paper, materials in the Ir–Ru–B system with nominal compositions of Ir–Ru–2B and 3Ir–Ru–4B were synthesized by arc melting and vacuum hot press (VHP) sintering. The phase composition and microstructure were characterized using X-ray diffraction, back scatter electron imaging, energy dispersive spectroscopy and electron back scatter diffraction. Different preparation processes for these Ir–Ru–B system materials were studied. The results show that Ir–Ru–2B prepared by arc melting and VHP sintering contains Ir(Ru)B 0.9 and Ru(Ir)B solid solutions, while 3Ir–Ru–4B contains Ir(Ru)B 0.9, Ru(Ir)B 2 and Ir(Ru) solid solutions. The error for the lattice parameters of the VHP sintered samples was larger than that of the arc melted samples. The energy spectrum analysis of the Ir–Ru–2B samples prepared using different processes indicates that the solubility of the solid solutions in the VHP sintered samples was higher than the solubility in the arc melted samples. The formation mechanisms for the (Ir, Ru)–B, (Ir(Ru)B 0.9, Ru(Ir)B 2 and Ru(Ir)B) and Ir(Ru) solid solutions are discussed in detail. There is more Ir(Ru) solid solution in the VHP sintered sample than in the arc melted sample, and the grain orientation of the former is more complex than that of the latter.