This paper describes the fabrication of porous poly(methyl methacrylate) (PMMA) and PMMA/TiO2 composite microspheres by electrospraying in a humid chamber. The effects of polymer concentration, co-solvent ratio, and relative humidity on morphology were evaluated to prepare microspheres with well-defined porous structures. Dichloromethane and hexanol were used as the solvent and co-solvent in solvent mixture for PMMA, respectively. The optimized conditions were established as 4 wt% for PMMA concentration, 10 wt% for hexanol ratio, and 60 % for relative humidity. The resultant PMMA microspheres exhibited a spherical morphology and a highly porous structure. Among the process variables, relative humidity was found to be a critical factor for the development of large surface pores. In addition, PMMA/TiO2 composite microspheres with a highly porous structure were prepared by simply mixing TiO2 nanopowders in a PMMA solution before electrospraying. Energy-dispersive X-ray spectroscopy confirmed that the TiO2 nanopowders were well distributed throughout the composite microspheres. Our results clearly indicate that porous PMMA and PMMA/TiO2 microspheres have potential uses as catalyst carriers, sensors, and in cosmetics, among other possibilities.