Porous silk fibroin (SF) microparticles were prepared by a simple one-step water-in-oil emulsification-diffusion method. Aqueous SF solution and organic phase solvent were used as water and oil phases, respectively. Four organic solvents with different water solubility were studied, i.e., ethyl acetate, diethyl ether, dichloromethane, and chloroform. Influences of organic phase solvent, water/oil volume ratio, and SF concentration on SF microparticle characteristics were investigated. It was found that shape of the SF microparticles depended upon the type of organic phase solvent. The SF microparticles with hollow or bowl-like shape were fabricated when organic solvents with higher water solubility, which are ethyl acetate and diethyl ether, were used as the continuous oil phase. While using organic solvents with lower water solubility, i.e., dichloromethane and chloroform resulted in the spherical shape SF microspheres. The water/oil volume ratios and the SF concentrations did not affect on the bowl-like and spherical shapes of SF microparticles. Results from scanning electron microscope shows that all the SF microparticle matrices were porous structures. Using ethyl acetate and diethyl ether as the oil phase gave larger SF microparticle sizes than using dichloromethane and chloroform. The influences of water/oil volume ratio and the SF concentration showed slightly effect on the sizes of SF microparticles. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1127-1133, 2010