HMO1 proteins are abundant Saccharomyces cerevisiae (yeast) High Mobility Group Box (HMGB) proteins. HMGB proteins are nuclear proteins that are known to have an architectural function. HMO1 possesses two HMGB box domains. It has been reported that double box HMGB proteins induce strong bends upon binding to DNA. It is also believed that they play an essential role in reorganizing chromatin and therefore are likely to be involved in gene activation. To characterize DNA binding we combine single molecule stretching experiments and AFM imaging of HMO1 proteins bound to DNA. By stretching DNA bound to HMO1, we determine the dissociation constant and the cooperative parameter. Furthermore, we learn that HMO1 proteins form loops, and by pulling on these loops, we characterize the size of these loops and the average force to break a loop. Stretching experiments enable us to study the dynamics of loop formation and the time for reformation of these loops after they are pulled apart. AFM images are used to probe the conformations of individual HMO1-DNA complexes. The results show that at lower concentrations, HMO1 preferentially binds to the ends of the double helix and links separate DNA strands, forming bridges. At higher concentrations HMO1 induces formation of a complex network that reorganizes DNA. Taken together, these results suggest that both HMG boxes of HMO1 participate in multiple functions in vivo.