The coassembly behavior of thermoresponsive statistical copolymers and a double hydrophilic block copolymer having a permanently hydrophilic block and a thermoresponsive block is investigated. By adjusting the hydrophilicity of the thermoresponsive statistical copolymers, hybrid nanoparticles are obtained with various ratios of the two species. Importantly, the size of these nanoparticles can be controlled in between 40 and 250 nm dependent on the To, and the amount of statistical copolymers in the solution. Simultaneous analysis of static and dynamic light scattering data indicates that the possible structure of nanoparticles varies from hard sphere to less compact architecture and most probably depends on a difference between cloud point temperatures of individual components. This developed coassembly method provides a simple platform for the preparation of defined polymeric nanoparticles.