The 300 bp upstream fragment of cpcβ gene which encodes the β-subunit of phycocyanin and the 1.4 kb fragment of glnA gene encoding glutamine synthetase were obtained by polymerase chain reaction (PCR) from genomic DNA of marine cyanobacterium Synechococcus sp. PCC 7002. Then, integrative expression vector pKGC-MT, which contained promoter Pcpcβ, mMT-Ⅰ gene and integrative platform glnA, was constructed and introduced into Synechococcus sp. PCC 7002 via natural transformation. Selected by ampicillin, the stable transgenic cyanobacterium was obtained. PCR analysis indicated the integration of mMT-Ⅰ gene in genomic DNA of Synechoccus sp. PCC 7002 and Western blotting demonstrated the expression of mMT-Ⅰ in the cyanobacterium. According to the result of ELISA, the amount of the expressed mMT-Ⅰ was about 800 μg/g fresh cells.