Tumor initiation and progression are critically dependent on interaction of cancer cells with their cellular and extracellular microenvironment. Alterations in the composition, integrity, and mechanical properties of the extracellular matrix (ECM) dictate tumor processes including proliferation, migration, and invasion. Also in primary liver cancers, consisting of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), the dysregulation of the extracellular environment by liver fibrosis and tumor desmoplasia is pertinent. Yet, in-depth characterization of liver cancer ECM and underlying tumor-promoting mechanisms remain largely unknown. Herein, we used an integrative molecular and mechanical approach to extensively characterize the ECM of HCC and CCA tumors by utilizing decellularization techniques. We identified a myriad of ECM-related proteins in both tumor and adjacent liver tissue, highlighting the complexity of the primary liver cancer matrisome. The differences in ECM protein abundance result in divergent mechanical properties on a macro- and micro-scale that is tumor-type specific. Furthermore, we employed the decellularized tumor ECM to create a tumor-specific hydrogel that support patient-derived tumor organoids. This provides a new avenue for personalized medicine by combining patient-derived tumor ECM and cancer cells. Taken together, this study provides better understanding of alterations to key aspects of the ECM that occur during primary liver cancer development.