TSG101 was identified as a tumor susceptibility gene by Stanley Cohen. In a variety of human cancers, no genomic deletion in TSG101 gene has been reported but many aberrant TSG101 transcripts has been found. Some studies have revealed that TSG101 participates in MDM2/p53 regulatory circuitry¡Bmembrance trafficking and receptor recycling. Other reports also showed that TSG101 might be a transcription regulatory factor. However, mechanism of these TSG101 function awaits further characterization. To further scrutinize the function of TSG101 and its subcellular localization, a varieties of GFP-based recombinant plasmids which contain various length of TSG101 cDNA have been constructed and transfected into cells. Western blot analysis had shown that these constructs could express GFP-TSG101 fusion protein of expected size. The fluorescence and confocal microscopy have shown that wild type TSG101 localized in ER, Golgi and endosome compartments, also amino acid residues 136-233 and 316-390 of TSG101 are two important regions for its subcellular localization. Previous reports had shown that TSG101 interact with OP18 which is an important regulator for spindle formation in M phase. To elucidate the localization of TSG101 and OP18 in M phase cell, we have cloned OP18 and generate GST-OP18 fusion protein for anti-OP18 antiserum production.Then, pDsRed-OP18 fusion protein expressed in OP18/pDsRed recombinant plasmid transfected cell was detected by western blotting analysis using this anti-OP18 antiserum. The subcellular localization of DsRed-OP18 and GFP-TSG(1-390) fluorescence were recorded in double transfected cells which were arrested in M phase by nocodzole treatment. We observed the evenly distribution of pDsRed-OP18 red fluorescence and punctate vesicular localization of GFP-TSG(1-390) green fluorescence. Whether these two protein interact functionally awaits further investigation.