This study presents a novel method for the preparation of hydrophilic drug-encapsulated solid lipid microcapsules (SLMCs) with a narrow particle size distribution for drug delivery systems via solid-in-oil-in-water (S/O/W) dispersions by premix membrane emulsification and subsequent solidification of the oil phase in the S/O/W dispersion. The primary aspect of this work is to form nano-order solid particles of hydrophilic drugs in solid lipids and the secondary is to encapsulate of the nano-order particles in size-controlled lipid microcapsules. The prepared capsules had a matrix type structure composed of a high-melting triglyceride, glycerol trimyristate with a melting point of 55 degrees C. In the lipophilic matrix of the capsule, nano-order particles of a hydrophilic drug, vitamin B-12 (VB12) were embedded. Initially, a solid-in-oil (S/O) dispersion was prepared by water removal of the water droplets containing 1.1 wt.% VB12 in a water-in-oil emulsion preliminary prepared, followed by mixing with an external water phase at 60 degrees C to form a coarse S/O/W dispersion. By forcing the resultant S/O/W dispersion through a Shirasu porous glass (SPG) membrane with a mean pore diameter of 14.8 mu m at this temperature under a transmembrane pressure of 25 kPa, uniformly sized S/O droplets were formed at a very high transmembrane flux (11.8 m(3) m(-2) h(-1)). Subsequent solidification of the oil phase in the S/O/W dispersion resulted in SLMCs with a mean particle diameter of 15.4 mu m and a high encapsulation efficiency (up to 93.5%). In premix membrane emulsification the transmembrane pressure affected the properties of the S/O/W dispersion and the resultant SLMCs. At the higher transmembrane pressures, smaller S/O droplets with broader size distributions and lower encapsulation efficiencies were produced, due to the higher shear stresses inside the membrane pores. The particle size of SLMCs was controlled by adjusting the membrane pore size and transmembrane pressure in premix membrane emulsification. (C) 2009 Elsevier B.V. All rights reserved.