The supersolubility data of Li2CO3 in the seeded aqueous solution were measured by focused beam reflectance measurement (FBRM). The effect of seed crystals on the supersolubility was investigated, where two kinds of seed crystals were considered, namely 2# seed with 318 mu m volume mean crystal size and 5# seed with 21 mu m volume mean crystal size, respectively. It was found that the supersolubility level of Li2CO3 in the presence of 2# seed is lower than that with 5# seed when using the same amount of seed; and with the increase of the seed loading, the supersolubility with 2# seed decreases slightly, whereas that with 5# seed becomes greater. The seeded supersolubility decreases when increasing both temperature and the stirring speed, and goes up with the increase of the feeding rate of Na2CO3. Moreover, by comparing the laser method with FBRM technology, FBRM is confirmed to be a better apparatus to detect the nucleation phenomena in the presence of seed. (C) 2009 Elsevier B.V. All rights reserved.