We designed a cascade spiral microfluidic device (i-Finity®)continuously isolated the unlabeled cancer cells from blood samples without lysing processes. The results showed that the i-Finity® device excluded a high percentage of RBCs in the first stagerecollected the cancer cells in the second stage. The i-Finity® device can efficiently enrich the cancer cells more than 1000 times in 10 minutes, which substantially curtailed sample preparation timeimproved the accuracy of diagnosis.