Osteosarcoma cells are capable of extracellular matrix (ECM) synthesis. The ability of ECM to trigger the proliferation of a novel osteosarcoma cell line (OSCORT) was tested in this study in relation to a known tumor ECM, isolated from Engelbreth—Holm—Swarm (EHS) sarcoma (EHS-ECM). OSCORT was grown in monolayer, in EHS-ECM and in ECM deposited by the cells (OSCORT-ECM). Both EHS-ECM and OSCORT-ECM increased the proliferation and migration of OSCORT cells. Among the ECM biopolymers, heparan sulfate proteoglycan (HSPG) and fibronectin enhanced invasive growth, collagen type IV reduced it, while laminin had no effect. Among the ECM components HSPG and collagen IV increased both the synthesis and activation of collagenase type IV, and all the ECM components substantially increased β1 integrin levels in the cells. The majority of ECM biopolymers decreased the level of topoisomerase I (except laminin) and elevated topoisomerase II (except fibronectin) in OSCORT. The switch in the ratio between the activities of topoisomerases I and II was mainly due to HSPG. The HSPG synthesized by OSCORT cells is described as agrin, which is a novel finding. The present study showed that HSPG (agrin) showed the most remarkable stimulatory action on the growth and migration of OSCORT cells. HSPG-induced topoisomerase II-induction deserves further experimentation, to discover its relevance to tumor progression.