Undifferentiated pleomorphic sarcoma (UPS) and malignant peripheral nerve sheath tumor (MPNST) are aggressive soft tissue sarcomas that do not respond well to current treatment modalities. The limited availability of UPS and MPNST cell lines makes it challenging to identify potential therapeutic targets in a laboratory setting. Understanding the urgent need for improved treatments for these tumors and the limited cellular models led us to generate additional cell lines to study these rare cancers further. Patient-derived tumors were used to establish 5 new UPS models, including one radiation-associated UPS: UPS060.1, UPS271.1, UPS511, UPS0103, and RIS620; and 3 new models of MPNST: MPNST007, MPNST3813E, and MPNST4970. This study examined the utility of the new cell lines as sarcoma models by assessing tumorigenic potential and mutation status for known sarcoma-related genes. All the cell lines formed colonies and migrated in vitro. The in vivo tumorigenic potential of each cell line was determined by either subcutaneous injection of cells or implantation of tumor tissue into immunocompromised mice. UPS060.1, UPS271.1, and UPS511 cells formed tumors in mice upon subcutaneous injection. UPS0103 and RIS620 tumor implants formed tumors in vivo, as did MPNST007 and MPNST3813E tumor implants. Mutation analysis of a panel of genes frequently mutated in sarcomas showed that two of the three MPNST cell lines had NF1 mutations. Two of the three MPNST cell lines had mutations in polycomb repressive complex 2 members. These new cellular models provide the scientific community with powerful tools for detailed studies of sarcomagenesis and investigate novel therapies for UPS and MPNST.