Objective To clarify the possible gene mutations in luteinizing hormone(LH) receptor gene in a boy with LH independent precocious puberty and probe the mechanism the of diseases caused by LH receptor activating mutations. Methods ( 1 ) Describe the clinical manifestations and laboratory data in a 5-year-old boy with LH independent precocious puberty. (2) Peripheral leukocytes were collected from the proband, his parents and other 20 normal puberty developed males. PCR and direct DNA sequence of 11 exons in LH receptors gene were conducted. Results (1) The proband was diagnosed to have LH independent precocious puberty according to the clinical symptoms and the laboratory tests. (2) A germ-line heterozygous point mutation in the 11 exon of LH receptor gene was found in the proband and his mother:c1193 T→C leading to amino acid change with M398T, which causes consecutively an activation of the LH receptor. (3) Other nucleotide changes in the proband and other normal males include c935 A→ G (N312S) and c1065 T→C(same sense mutation). Conclusions (1) A germ-line heterozygous point mutation in the LH receptor gene with M398T leads to consecutively activation of the LH receptor and LH independent precocious puberty. (2) The same point mutation does not have any influence on the puberty development, menstruation and productive functions of the proband's mother. (3) The LH receptor gene has possible polymorphism in the Han ethnic population.