Three-dimensional (3D) printing has emerged as a promising technique for creating in vitro tumor models that replicate the tumor microenvironment, with the potential to reduce or replace the use of experimental animals. The incorporation of 3D decellularized extracellular matrix (dECM) hydrogels significantly enhances cellular responsiveness and functionality in drug screening. However, the limited printability of dECM restricts its application in ex vivo 3D disease models. To address this limitation, researchers have developed a blended bioink composed of dECM, gelatin methacrylate (GelMA), and gelatin, specifically tailored for direct ink writing-based 3D bioprinting. This formulation exhibits favorable shear-thinning behavior, enhanced viscosity, and thermal-sensitive properties, making it suitable for 3D bioprinting. The combination of dECM with GelMA and gelatin not only improves the printability of the bioink but also enhances the resolution of the printed scaffolds. Furthermore, dECM demonstrated positive effects on human hepatocellular carcinoma (HepG2) cells, promoting proliferation, migration, and cell spheroid formation. A 3D liver cancer model was successfully created in vitro by printing HepG2 cells encapsulated in the bioink containing dECM. This model exhibited characteristics akin to in vivo solid tumors, including notable cell proliferation, protein secretion, and substantial cell spheroid formation (up to 78.83 ± 9.41 μm on day 8). Additionally, it showed drug resistance, with 46.23% and 31.34% cell viability observed at 100 μg/mL concentrations of doxorubicin and paclitaxel, respectively. These findings underscore the potential of bioprinted 3D tumor models composed of GelMA, gelatin, and dECM as valuable platforms for the evaluation of anticancer drugs.