In order to further research the role of Sox9 in the development of the Siberian sturgeon (Acipenser baerii Brandt)’s lateral line neuromast, the full-length Sox9 cDNA of Siberian sturgeon had been successfully cloned by RT-PCR and rapid amplification of cDNA ends (RACE) methods. The full-length Sox9 cDNA of Siberian sturgeon had 1 409 bp, which consisted of a 1 083 bp open reading frame (ORF) encoding 360 amino acids, a 19 bp 5′untranslated region (5′UTR) and a 307 bp 3′untranslated region (3′UTR). The molecular weight of this mature peptide was estimated to be 41 221.7U. Neighbor-Joining (NJ) method had been used for multiple alignment analyses, and Siberian sturgeon was closest to Amur sturgeon (Acipenser schrenckii). The Siberian sturgeon’s Sox9 gene was high conservative to other species. These results were much similar to other studys that had already been done in Blue tilapia (Oreochromis aurea), Yellow catfish (Pelteobagrus fulvidraco) and Swamp eel (Moncpterus albus)〖WTB1〗. Meanwhile, in order to study the connection between the feature of the expression of the Sox9 to the development of the Siberian sturgeon’s lateral line neuromast, The fluorescent quantitative RT-PCR analysis had been used for detecting Sox9 relative expression levels in the different tiusses and different embryonic development stages. Sox9 had relatively low expression levels in liver, pancreas, kidney and muscle. However, in the brain, Sox9 had very high expression levels, and the relative expression levels of the brain reached to 8.9 times the quantity of the relative expression in the pancreas and to 21 times the quantity of the relative expression in the kidney. In the different stages of the Siberian sturgeon embryonic development, Sox9 expression had different relative expression levels. Its relative expression had no major differences and reached to relatively high in gastrula stage, neurula stage and formation of visual bubble. Especially in the gastrula stage and neurula stage, Sox9 relative expression reached to 1.2 times and 1.4 times the quantity of formation of heart. All of these results were nearly same as the resaeches of zebrafish (Danio rerio), chicken (Gallus gallus) and mouse (Mus musculus). At the same time，the expression features showed Sox9 might play a very important roles in the development of the neuromast of the Siberian sturgeon which already had found in the development processes of the zebrafish neuromast. This research will lay a foundation for the future study on the role of Siberian sturgeon’s Sox9 gene in the differentiation of lateral line ganglion development, cells migration processes and so on. At the same time, the study on the role of the Sox9 in the cell signaling patheway of the development of the Siberian sturgeon’s lateral line neuromast is required too.