Background: Molecular characteristics hold substantial clinical significance in cancer. Previous research has elucidated the molecular classification of gastrointestinal (GI) cancers, leveraging biomarkers like gene alterations, MSI, EBV status, and chromosomal instability. However, most of these studies relied on tissue biopsies. Limited investigations have been documented regarding the characterization of molecular profiles through liquid biopsy. Here we present a comprehensive genomic profiling study conducted on advanced GI cancer patients using blood samples. Methods: This prospective study is a part of a global initiative focused on molecular biomarker screening across various solid tumors. Here we report the early result of 106 unresectable GI cancer patients, encompassing those with advanced disease or experiencing relapse after prior treatments. The cohort comprises 66 colorectal cancer (CRC) patients, 34 gastric cancer (GC) patients, and 6 esophageal cancer (EC) patients. Each patient contributed a 10-mL blood sample for comprehensive circulating tumor DNA (ctDNA) analysis. The study employed PredicineCARE, a 152-gene, NGS-based liquid biopsy assay, to profile somatic gene variations within this patient population. Results: The study revealed a total of 1,597 somatic mutations, with 1,077 occurring in CRC, 448 in GC, and 72 in EC. Additionally, 722 gene copy number variants were identified, with 288 in CRC, 351 in GC, and 83 in EC patients. In CRC, the most frequently altered genes (prevalence > 20%) included TP53 (58%), APC (45%), KRAS (33%), and BRCA2 (22%). Conversely, in GC, the most altered genes were TP53 (59%), TERT (35%), FAT1 (29%), ARID1A (26%), and FGFR4 (24%). Among the 6 EC patients, 3 carried TP53 variations, with variations in APC (N=2), ERCC5 (N=2), FAT1 (N=2), and EGFR (N=1) also observed. The mutation burden in CRC (median 3.73 mut/Mb) and GC (median 3.57 mut/Mb) displayed no significant differences. However, the mutation burden in CRC was significantly higher than that in EC (2.24 mut/Mb) (p=0.04). A similar pattern was observed between GC and EC but did not reach statistical significance (p=0.10) due to limitations in cohort size. Furthermore, the assay identified patients carrying both germline and somatic mutations related to homologous recombination deficiency (HRD). In CRC patients, 5 had MLH1 germline mutations, 6 had MSH2 mutations (5 were germline), 4 had MSH6 germline mutations, 2 had PMS2 somatic mutations, and 1 had an EPCAM germline mutation. While in GC patients, 2 had MLH1 germline mutations, 1 had an MSH6 mutation, and 1 had a PMS2 somatic mutation. Conclusions: This study elucidated the comprehensive mutational landscape of advanced gastrointestinal cancer through liquid biopsy, thereby contributing novel biomarkers for clinical diagnosis and facilitating targeted therapy mechanism investigations.