Abstract: In Synechocystis sp. PCC6803, gene knock-out is the most straightforward and effective method to reveal the physio-logical function of a gene. Nevertheless, insertion mutants could not be generated for those genes essential to survival. In order to elucidate the function of such genes in Synechocystis sp. PCC6803, a copper-induced gene expression platformwas constructed using the promoter of petE ( ). PpetE from Synechocystis sp. PCC6803 and the beta-galactosidase gene (lacZ) from E.coli GM48 were cloned respectively by doing polymerase chain reaction ( PCR), and the PpetE was positioned upstream of lacZ. The PpetE–lacZ construct was integrated into the genomeof Synechocystis sp. PCC6803 via homologous recombinations. The expression of beta-galactosidase gene was found to be controllable by adjusting the concentration of Cu2+in medium. In a range from 6 to 400nmol/L, Cu2+induced the expression of beta-galactosidase in an S-shaped curve, but when the concentration of Cu2+in medium was below 6nmol/L or above 400nmol/L, the activity of beta-galactosidasewas either too low to be detected or too high to be regulated. This copper-induced gene expression platform can be used in the control of some indispensable genes in Synechocystis sp. PCC6803: cells survived in the presence of Cu2+, so that the physiological effect of a gene could be observed when Cu2+is removed.