We present a concept of the sol-gel reactor with injection of stock solutions through a T mixer, environmental gas control, thermal control of the reactive medium and in-situ particle size measurement using a monomode optical fibre probe. The rapid injection of the whole amount of reagents leads to short time of nucleation, and the micromixer eliminates gradients of concentrations, which results in higher local nucleation and aggregation rates. The reactor is used for production of mono-disperse nanometric titanium oxide sols. With this reactor, induction kinetics are reproducible and agree with a model describing the mean particle size increase by a slow aggregation process. As well as the in-situ size measurement technique, the reactor is a kinetic tool for determination of the sol aggregation rate. As the rules for scale-up of its equipment are already established, it is of interest for the operation and the design of industrial-scale sol-gel reactors.