Electrospinning is one of the simple techniques for the production of polymer nano-microfibers. In this study, hollow fibers from poly(methyl methacrylate) (PMMA) were formed by electrospinning under pressurized carbon dioxide (CO2) in a single processing step. The experiments were conducted at temperatures and pressures in the range 27-37 degrees C and 4-6 MPa, respectively. At 5 MPa, CO2 seemed to have enough affinity to dissolve a portion of dichloromethane (DCM) to assist its evaporation. Under subcritical CO2, electrospun products with hollow core fibers having diameters of 4-16 m were generated. The results confirmed that the change of operating parameters had a strong influence on the morphologies (crack or hollows) of the electrospun products. This study demonstrated that this process offers the possibility that electrospinning under pressurized CO2 will become an essential and useful method for the generation of polymer structures with hollow interiors. POLYM. ENG. SCI., 56:752-759, 2016. (c) 2016 Society of Plastics Engineers