Synthetic genes are very useful in genetic and protein engineering. Here we propose a general method for construction of synthetic genes. Short oligonucleotides are joined through ligase chain reaction (LCR) in high stringency conditions to make "unit fragments" which are then fused to form a full-length gene sequence by polymerase chain reaction. The procedure is simple and accurate and does not place constraints on sequence and length. In this report, a recombinant leptin gene was synthesized according to the codon preference of Escherichia coli. Besides, a substitution of the only Met at position 54 for Leu and an addition of a Met at the N-terminus were introduced in the synthetic gene. The gene was cloned in the pQE-31 expression vector and was expressed in E. coli. A large amount of recombinant leptin containing 6 x His tag was produced and purified by Ni-NTA affinity column. Finally, intact leptin-L54 was released after removing the tag by CNBr cleavage at the Met residue.