MicroRNAs (miRNAs) are ~22-nucleotide noncoding RNAs that play a crucial role in regulating muscle development. Our previous study shows that miR-206 is specifically expressed in tilapia skeletal muscle, and exhibits a dynamic expression pattern at different developmental stages. Here, we reveal that miR-206 emerges as a crucial regulator of tilapia growth. miR-206 loss of function leads to the acceleration of tilapia growth. IGF-1 is identified as the target gene of miR-206. miR-206 directly changes IGF-1 expression by targeting its 3' UTR, and inhibition of miR-206 substantially increases the IGF-1 mRNA level in vivo. Thus, miR-206 could be developed as a molecular marker to assist fish breeding.