A new continuous precipitation process using a tubular reactor with a T-mixer was applied to the production of nanometer-to-micrometer particles of several kinds of inorganic salts. A reactor tube was placed in two constant-temperature baths at different temperatures for separating the particle formation and growth stages. This enabled good monodispersity and high yield simultaneously. Another reactor setup using a reactor tube of submillimeter diameter with a rapid particle sampler was applied for investigating particle growth in the initial stage. By varying the residence time from 0.4 ms to 120 s over six orders of magnitude, lanthanum phosphate particles of diameter 3 nm to 1 mu m were obtained. At 0.4 ms, the particle size widely ranged from 3 to 200 nm since the nucleation was continuing. After the nucleation practically ended at arround 10 ms, the particle grew uniformly by crystal growth. The shape became spherical and the size distribution became more monodisperse. The typical final geometric standard deviation was 1.1. Using the thin tubular reactor, the quality of the resulting particles was improved as well as the observation of particle growth in the initial stage being made possible.