Cancer stem cells play a crucial role in tumor initiation, metastasis and therapy resistance. Cellular heterogeneity and plasticity challenge the isolation of cancer stem cells. The impact of intratumoral cellular heterogeneity in the context of treatment resistance using a label-free approach remains understudied. Here, we use the sedimentation field-flow fractionation technique to separate, without labeling, cell subpopulations of colorectal cancer cell lines and primary cultures according to their biophysical properties. One of the three cell subpopulations sorted by SdFFF exhibits cancer stem cell traits, including high tumorigenicity in vivo, and a higher frequency of tumor-initiating cells compared to the other subpopulations. In vitro two- and three-dimensional chemosensitivity assays emphasize the therapeutic relevance of this cancer stem cell-like subpopulation due to its chemoresistance. Therefore, our findings highlight a label-free cell sorting approach to reveal intratumoral cellular heterogeneity and its implication in therapy resistance. This approach enables the study of the individualized response of each sorted cell subpopulation by breaking down the tumor, thus offering new perspectives for personalized therapy.