The validity of utilizing microspace for nanoparticles production was investigated by using a newly proposed microdevice. The proposed reactor consists of same axle dual pipes, and this assembly gives a microspace by an annular laminar flow of two immiscible liquids. We tried to produce titania particles by supplying tetraisopropoxide (TTIP) solutes to the inner tube and isopropanol/water mixture to the outer tube. Mono-modal spherical particles of titania with narrow size distribution were successfully produced without precipitation of the particles at the wall. It was also found that the particle size was possible to control in the range from 40 to 150 nm only by changing the diameter of the inner tube at a low TTIP concentration. Thus, the proposed concept was confirmed to be valid for the production of nanoparticles. (C) 2003 Elsevier B.V. All rights reserved.