The aim of this contribution is to determine the relationship existent between the chemistry and/or viscosity of some biodegradable polymer solutions and the morphology of micro- and nanospheres resulted after spray drying the solutions at room conditions either in the presence or in the absence of an encapsulated aqueous material. Using dichloromethane as solvent, the following polyesters were used to prepare 2 wt% solutions: polyhydroxybutyrate (PHB), polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA) and Eastar Bio GP (GP). A comprehensive thermal characterization was also performed on all polymers to verify the relationships existent between the structure of polyesters and certain important parameters, such as T(g), T(m), T(d). It was observed that a decrease in the solution viscosity triggers the formation of smoother microspheres. When the viscosity becomes low enough the sprayed solution can lead to the development of well defined nanospheres instead of microspheres. Additionally, it was found that in the presence of an aqueous core the micro- and/or nanocapsules coalesce into larger micrometric aggregates, due to the plasticizing effects of water on the polyester.