Phylogenetic diversity of Form I and Form II ribulose1, 5-bisphosphate carboxylase/oxygenase (RubisCO) largesubunit (rbcL) genes in the inshore and offshore areas of the East China Sea were investigated. Two new primer setswere designed for amplifying partial sequences of rbcL genes from Proteobacteria. Four rbcL gene clone libraries wereconstructed by amplification and cloning of approximately 640~800 bp sequences of bacterioplankton populations.The method of screening library by denaturing gradient gel electrophoresis (DGGE) was introduced. The resultsshow that the diversity of Form I is higher in offshore waters with higher salinity and lower productivity, while thatof Form II is higher at the inshore station where salinity is lower and productivity is higher. Several clusters ofsequences obtained are deeply rooted and show low similarity (60%~78%) to the known rbcL in existing databases.The degree of diversity of rbcL genes is directly related to environmental variables, including temperature, salinity,pH, dissolved oxygen, etc. These results indicate that rbcL gene can be used as an effective indicator for geneticdiversity and population variability of bacterioplankton with the ability of carbon dioxide fixation in the sea. Phylogenetic diversity of Form I and Form II ribulose1, 5-bisphosphate carboxylase / oxygenase (RubisCO) largesubunit (rbcL) genes in the inshore and offshore areas of the East China Sea were investigated. Two new primers setswere designed for amplifying partial sequences of rbcL genes from Proteobacteria. Four rbcL gene clone libraries were constructed by amplification and cloning of approximately 640-800 bp sequences of bacterioplankton populations. The method of screening library by denaturing gradient gel electrophoresis (DGGE) was introduced. The resultsshow that the diversity of Form I is higher in offshore waters with higher salinity and lower productivity, while that of Form II is higher at the inshore station where salinity is lower and productivity is higher. Several clusters of sequences are seen deeply rooted and show low similarity (60% -78%) to the known rbcL in existing databases. The degree of diversity of rbcL genes is directly related to environmental variables, including temperature, salinity, pH, dissolved oxygen, etc. These Results indicate that rbcL gene can be used as an effective indicator for genetic diversity and population variability of bacterioplankton with the ability of carbon dioxide fixation in the sea.