Synechocystis sp. PCC 6803 is an attractive host for bio-ethanol production. In the present study, a nitrogen starvation approach was applied on an ethanol producing strain for inhibiting the growth, since ethanol production competes with the cell growth. The effect of gene deletions in the glycogen and polyhydroxybutyrate (PHB) synthesis pathways was investigated. Measurements of intracellular glycogen and PHB revealed that the glycogen was accumulated under the nitrogen starvation condition and the gene deletion of glycogen synthesis pathway caused the accumulation of PHB. The ethanol producing strain harboring deletions for both the glycogen and the PHB synthesis pathways (ΔglgCΔphaCE/EtOH) produced ethanol at the specific rate of 240mgg (dry cell weight) day under the nitrogen starvation condition. In a high cell density culture (OD=50) using this ΔglgCΔphaCE/EtOH strain, the ethanol production rates were 1.08 and 2.01gL day under light conditions of 40 and 80μmolms, respectively.