Disclosed is a contact material for vacuum circuit breakers and a manufacturing process thereof. The contact material includes a copper component, a chromium component and a bismuth component, and has a metallographic structure comprising: a first phase including the copper component and the bismuth component; and a second phase including the chromium component and interposed among the first phase. In this structure, the boundary surface between the first phase and the second phase appears in a structural cross section of the alloy composition as a substantially smooth boundary line, such that when a segment of the boundary line is defined by two arbitrary points which lie on the boundary line at a straight distance of 10 .mu.m, the ratio of the length of the segment to the straight distance of 10 .mu.m lies within a range of approximately 1.0 to 1.4. Moreover, the boundary line may be approximate to a circle such that the ratio of the length of the boundary line to the length of the circumference of an ideal circle having the same area as the area defined by the boundary line lies within a range of approximately 1.0 to 1.3.In the above contact material, the chromium component is preferably included at a content of approximately 20 % to 60% by weight, and the ratio of the bismuth component to the sum of the bismuth component and the copper component preferably lies within a range of approximately 0.05% to 1.0% by weight.