The noninvasive detection of tumor cells is significantly important for early diagnosis of cancers and monitoring of their progress. Herein, we have developed a novel aptamer-based isothermal exponential amplification reaction (EXPAR) for sensitive detection of tumor cells. In this new assay, biotinylated sgc8c DNA aptamers are immobilized on streptavidin-coated magnetic beads. After incubation with target CCRF-CEM cells and magnetic isolation, the tumor cells are detected by translating the structure-switching of an aptamer upon tumor cell binding into an input of DNA trigger for EXPAR. Since more and more specific aptamers towards different tumor cells would be identified in the future, our strategy can be easily extended to the detection of different tumor cells just by simply altering the corresponding aptamers. Therefore, this EXPAR-based strategy may serve as a generic platform for the accurate detection of tumor cells, which has great potential for the early diagnosis of cancers.