The separation of cancer cells from blood samples is one of the most crucial tasks in cancer research. However, existing methods tend to be expensive and labor intensive. Accordingly, the present study proposes a low-cost platform that uses hydrodynamic effects for the label-free separation of cancer cells from whole blood samples using a simple centrifugal microfluidic device consisting of a Y-shaped microchannel, a contraction–expansion array (CEA) microchannel, and a bifurcation region. To enhance the separation efficiency, the input branches of the Y-shaped microchannel are designed with different widths to generate a sheath flow rate greater than the sample flow rate. As the sample flows through the CEA microchannel, the cancer cells are separated from the blood cells through inertial effects and the bifurcation law. Finally, the cancer cells are collected from the low-flow-rate branch of the bifurcation region. The feasibility of the device is first demonstrated by numerical simulations. Experimental trials are then performed to separate K562 cancer cells from blood samples with various hematocrit concentrations at disk rotational speeds ranging from 1000 to 3000 rpm. The experimental results show that the cancer cells can be successfully separated from a diluted blood sample with a ratio of 1:1.2 × 10⁵ K562 cells to blood cells with a high efficiency of 90% at an angular velocity of 2000 rpm.