Objective To refine the loss of heterozygosity (LOH) on chromosome 7q21－22 and identify the new tumor suppressor gene(s) in colorectal tumorigenesis. Methods Fifteen polymorphic microsatellite markers were analyzed on chromosome 7 and another 5 markers were applied on chromosome 7q21-22 region in 83 cases of colorectal cancer and normal DNA by PCR. PCR products were electrophoresed on an ABI Prism 377 DNA sequencer. GeneScan 3.1 and Genotyper 2.1 software were used for LOH scanning and analysis. Results A distinct region of frequent allelic deletion was observed on chromosome, another 5 polymorphic microsatellite markers were applied to 7q21-22 and the minimal region of frequent LOH was established on 7q21-22 spanning the D7S657, D7S646 locus. Conclusion Through detailed deletion mapping studies, a critical and precise region spanning the D7S657, D7S646 locus is identified, which must contain one or more unknown tumor suppressor gene(s) on colorectal cancer.