To break oil-in-water emulsions with an average oil droplet size of <2 mu m, a series of hyperbranched polyglycerol (HPG)-based demulsifiers methacrylated hyperbranched polyglycerol (HPG-MA) are synthesized successfully by controlling the ratio of HPG to glycidyl methacrylate (GMA). Dosage, temperature, settling time, and salinity are taken into account to evaluate the performance of these demulsifiers, respectively. The oil removal ratio with the addition of HPG-MA demulsifier can exceed 86% within 40 min to reach the equilibrium of demulsification, in comparison with 90 min for previously reported demulsifiers. Because of the specific branched structure, the demulsifier can multipointly adhere to the oil/water interface, and then shorten the time of adsorption and increase the rupture rate of oil droplets. The oil water interfacial tensions with the demulsifier in the water phase are further measured to help comprehend the demulsification mechanism. The change of oil droplet size against time, which reflects flocculation and coalescence of oil droplets, is vividly monitored during the process of demulsification. The demulsification performance indicates that the novel HPG-MA demulsifier displays great promise in the petroleum industry.