The 2’-5’ oligoadenylate synthetases (OAS) are important components of the innate immune system that recognize viral double stranded RNA (dsRNA). Upon dsRNA binding, OAS generates 2'-5'-linked oligoadenylates (2-5A), that activate ribonuclease L (RNase L) halting viral replication. The OAS/RNase L pathway is thus an important antiviral pathway and viruses have devised strategies to circumvent OAS activation. OAS enzymes are divided into four classes according to size: small (OAS1), medium (OAS2) and large (OAS3) that consist of one, two and three OAS domains respectively, and the OAS-like protein (OASL) that consists of one OAS domain and tandem domains similar to ubiquitin. Early investigations of the OAS enzymes hinted at the recognition of dsRNA by OAS, but due to size differences amongst OAS family members combined with the lack of structural information on full-length OAS2 and OAS3, the regulation of OAS catalytic activity by dsRNA is still not well understood. In particular, little is known about the structure, domain organization and hydrodynamic properties of OAS2. This is mostly due to the lack of well-established OAS2 expression systems and poor protein yield obtained from standard OAS2 expression from insect cells. Here I report expression and purification of OAS2 in human embryonic kidney cells. Following OAS2 purification, I investigated its dsRNA substrate specificity relative to OAS1. Activation assays with dsRNA suggested that OAS2 recognizes dsRNA greater than 35 base pairs. Further, I present the first low resolution structure of OAS2 obtained by small angle X-ray scattering that shows OAS2 exists as a high-affinity dimer. Using an integrated approach involving analytical ultra-centrifugation, dynamic light scattering and multi-angle light scattering I determined the hydrodynamic parameters and absolute molar mass of OAS2. This is followed by the computational model generation of dsRNA-OAS2 complex using dsRNA-OAS1 as restraints. Together, these results help us to better understand OAS2 domain organization, the features of dsRNA binding and the mechanism of 2-5A chain formation in OAS enzymes, further enhancing our understanding of how OAS discriminate self RNA from viral RNA. Together this work contributes to our understanding of the diverse roles OAS enzymes play in the innate immune system.