The cubic C15b (AuBe 5) type YbCu 5 has been prepared for the first time in a single phase by a high-pressure apparatus. Its magnetic susceptibility, high field magnetization, specific heat and electric resistivity reveal that this compound belongs to the characteristic dense Kondo system. Preparation of cubic C15b (AuBe 5) type YbCu 5 allowed us to discuss the physical properties of the pseudobinary system YbCu 5 − x Ag x in the whole composition region 0 ≤ x ≤ 1.