Nanoparticle synthesis is part of an emerging field in nanotechnology. Applications take advantage of the high surface area and confinement effects, which lead to nanostructures with properties different from those of conventional materials. The main focus of this work was on nanoparticle synthesis by the use of microemulsions. Change in nanoparticle size due to change in salinity concentration and type of microemulsion was explored. Titanium dioxide was prepared by a precipitation technique in which TiCl, was solubilized in the microemulsion system of n-heptane/water/NaCl/sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and reacted with NH4OH at a controlled temperature of 30degreesC. The results showed that different types of microemulsions produced titanium dioxides with different characteristics including different particle sizes. Increasing NaCl concentration strongly influenced the micellar size in both o/w and bicontinuous microemulsions, but it has only a slight effect in w/o microemulsions. Increasing TiCl4 concentration decreased micellar size in all types of microemulsions. The TiO2 obtained from an o/w microemulsion had a surface area and particle size similar to those of the commercial titanium dioxide, P25. For a bicontinuous microemulsion, titanium dioxide product was polydisperse with various particle sizes. Titanium dioxide synthesized in w/o microemulsions was smallest in particle size and highest in specific surface area. The particles were highly crystalline and only anatase phase was obtained in high salt concentrations.