SCAR is the first cancer database combining single-cell transcriptome and spatial transcriptomic datasets covering the most cancer types, with 348 cancer subtypes available to date. Furthermore, SCAR includes the spatial transcriptomic data of 21 organs and 34 types of single-cell omics techniques. On the other hand, SCAR also provides a wide range of analytical and visualization tools in tumor cell types classification, biomarker selection, survival curve prediction etc. It will allow users to comprehensively evaluate the tumor microenvironment and immunological response for cancer studies.