The full length cDNA of LH has been cloned from pituitary of half smooth tongue sole C. Günther by using RACE technology for the first time. The cDNA of LH is 670 bp，and the open reading frame is 477 bp encoding peptides of 158 amino acid. Multiple amino acid sequences alignments were performed among vertebrates，and the results showed that tongue sole LH mature peptide was the most similar to their orthologs of Pleuronectiformes and Perciformes which was 58 %～68 % identity. And 12 conserved cysteine residues and 1 N-linked glycosylation site were found in the deduced amino acid sequence. Real-time PCR analysis showed that LH mRNA was expressed in all twelve tissues including brain，pituitary，ovary and so on. The highest expression level was in pituitary. And the stronger amplification signals were detected in the brain and gonad than all other non- pituitary tissues. It suggested that LH may had the more physiological functions because LH mRNA of tongue sole expressed widely in non-pituitary tissues. Quantitative real- time PCR was used for analyzing the expression of female C. semilaevis LH mRNA in the reproductive cycle. The results showed that LH mRNA was expressed in all three tissues including brain，pituitary and ovary from the stage Ⅱto stage Ⅵ， and the highest expression level appeared on the stage Ⅳ and stage Ⅴwhich suggested that the main function of LH is to promote eggs finally mature and discharge. Radio immunoassay （RIA）marked by ¹²⁵I was used to detect the concentration of plasma LH in C.semilaevis. The results showed that the biggest plasma LH concentration appareed on the stage of Ⅴwhich also suggested that the main function of LH was to promote eggs finally mature and discharge.